Presidency of James K. Polk

Polk and his cabinet, Front row (left to right): John Y. Mason, William L. Marcy, James K. Polk, Robert J. Walker; Back row (left to right): Cave Johnson, George Bancroft (James Buchanan is absent).

Polk governed with the help of his cabinet, in which he placed great importance. The cabinet regularly met twice a week, and Polk and his six cabinet members discussed all major issues during these meetings.[26] Despite his reliance on his cabinet, Polk involved himself in the minutiae of the various departments, especially regarding the military.[27]

In selecting a new cabinet, Polk generally heeded Jackson's advice to avoid individuals who were themselves interested in the presidency, though he chose to nominate Buchanan for the crucial and prestigious position of Secretary of State.[28][29] Polk respected Buchanan's opinion and Buchanan played an important role in Polk's presidency, but the two often clashed over foreign policy and appointments.[30] Polk frequently considered dismissing Buchanan from office, as he suspected Buchanan of placing his own presidential aspirations above service to Polk, but Buchanan always managed to convince Polk of his loyalty.[31]

Polk put together an initial slate of cabinet choices that met with the approval of Andrew Jackson, who Polk met with in January 1845 for the last time, as Jackson died in June 1845.[32] Cave Johnson, a close friend and ally of Polk, would be nominated for the position of Postmaster General.[32] Though Polk was personally close with the incumbent Navy Secretary, John Y. Mason, he replaced him after Jackson insisted that none of Tyler's cabinet be retained.[32] In his place, Polk selected George Bancroft, a historian who had played a crucial role in Polk's nomination.[32] Polk also selected Senator Robert J. Walker of Mississippi as Attorney General.[32]

However, after news of Buchanan's selection for State was leaked, Vice President Dallas (an in-state rival of Buchanan) and a slew of Southerners insisted that Walker receive the higher position at Treasury.[33] Polk instead chose to nominate Bancroft as a compromise at Treasury while nominating Mason as Attorney General and a New Yorker, William L. Marcy, as Secretary of War.[33] Polk had intended the Marcy appointment to mollify Van Buren, but Van Buren was outraged at the move, in part due to Marcy's affiliation with the rival "Hunker" faction.[33] Polk then further enraged Van Buren by finally choosing Walker for Treasury; Bancroft was shifted back to Navy Secretary.[34]

After the outbreak of the Mexican-American War, Polk shook up his cabinet, sending Bancroft to Great Britain as an ambassador, shifting Mason to his old position of Navy Secretary, and successfully nominating Nathan Clifford as Attorney General.[35]

According to a story told decades later by George Bancroft, Polk set four clearly defined goals for his administration:[25]

• Reestablish the Independent Treasury System.
• Reduce tariffs.
• Acquire some or all of Oregon Country.
• Acquire California and New Mexico from Mexico.

While his domestic aims represented continuity with past Democratic policies, successful completion of Polk's foreign policy goals would represent the first major American territorial gains since the Adams–Onís Treaty of 1819.[25]

Map of Mexico in 1845, with the Republic of Texas, the Republic of Yucatan and the disputed territory between Mexico and Texas in red. Mexico claimed to own all of Texas.

The Republic of Texas had gained independence from Mexico following the Texas Revolution of 1836, and, partly because Texas had been settled by a large number of Americans, there was a strong sentiment in both Texas and the United States for the annexation of Texas by the United States. During the transition period after the 1844 election, President Tyler sought to complete the annexation of Texas. Lacking a two-thirds majority, an earlier treaty that would annex the republic was defeated in the Senate. Tyler proposed that Congress accomplish annexation through a joint resolution.[43] Due to disagreements regarding the extension of slavery, Senator Benton of Missouri and Secretary of State Calhoun disagreed on the best way to annex Texas, and Polk became involved in negotiations to break the impasse.[43] With Polk's help, the annexation resolution narrowly cleared the Senate.[43]

In a surprise move two days before Polk's inauguration, Tyler extended to Texas a formal offer of annexation.[44] Polk's first major decision in office was whether to recall Tyler's emissary to Texas, who bore an offer of annexation based on that act of Congress.[45] Though it was within Polk's power to recall the messenger, he chose to allow the emissary to continue, with the hope that Texas would accept the offer.[45] Polk also retained the United States Ambassador to Texas, Andrew Jackson Donelson, who sought to convince the Texan leaders to accept annexation under the terms proposed by the Tyler administration.[46] Though public sentiment in Texas favored annexation, some Texas leaders disliked the strict terms for annexation, which offered little leeway for negotiation and gave public lands to the federal government.[47] Nonetheless, in July 1845, a convention in Austin, Texas ratified the annexation of Texas.[48] In December 1845, Polk signed a resolution annexing Texas, and Texas became the 28th state in the union.[49] The annexation of Texas would lead to increased tensions with Mexico, which had never recognized Texan independence.[50]

Map of Oregon Country, which the Oregon Treaty split between the Americans and British at the 49th parallel

Since the signing of the Treaty of 1818, the largely unsettled Oregon Country had been under the joint occupation and control of Great Britain and the United States. Previous U.S. administrations had offered to divide the region along the 49th parallel, which was not acceptable to Britain, as it had commercial interests along the Columbia River.[51] Britain's preferred partition, which would have awarded Puget Sound and all lands north of the Columbia River to Britain, was unacceptable to Polk.[51] Edward Everett, President Tyler's minister to Britain, had informally proposed dividing the territory at the 49th parallel with the strategic Vancouver Island granted to the British. However, when the new British minister Richard Pakenham arrived in Washington in 1844, he found that many Americans desired the entire territory.[52] Oregon had not been a major issue in the 1844 election, but the recent heavy influx of settlers to the Oregon Country and the rising spirit of expansionism in the United States made a treaty with Britain more urgent.[53]

Though both the British and the Americans sought an acceptable compromise regarding Oregon Country, each also saw the territory as an important geopolitical asset that would play a large part in determining the dominant power in North America.[51] In his inaugural address, Polk announced that he viewed the American claim to the land as "clear and unquestionable", provoking threats of war from British leaders should Polk attempt to take control of the entire territory.[54] Polk had refrained in his address from asserting a claim to the entire territory, which extended north to 54 degrees, 40 minutes north latitude, although the Democratic Party platform called for such a claim.[55] Despite Polk's hawkish rhetoric, he viewed war with the British as unwise, and Polk and Buchanan opened up negotiations with the British.[56] Like his predecessors, Polk again proposed a division along the 49th parallel, which was immediately rejected by Pakenham.[57] Secretary of State Buchanan was wary of a two-front war with Mexico and Britain, but Polk was willing to risk war with both countries in pursuit of a favorable settlement.[58]

In his December 1845 annual message to Congress, Polk requested approval of giving Britain a one-year notice (as required in the Treaty of 1818) of his intention to terminate the joint occupancy of Oregon.[59] In that message, he quoted from the Monroe Doctrine to denote America's intention of keeping European powers out, the first significant use of it since its origin in 1823.[60] After much debate, Congress eventually passed the resolution in April 1846, attaching its hope that the dispute would be settled amicably.[61] When the British Foreign Secretary, Lord Aberdeen, learned of the proposal rejected by Pakenham, Aberdeen asked the United States to re-open negotiations, but Polk was unwilling to do so unless a proposal was made by the British.[62]

With Britain moving towards free trade with the repeal of the Corn Laws, good trade relations with the United States were more important to Aberdeen than a distant territory.[63] In February 1846, Polk allowed Buchanan to inform Louis McLane, the American ambassador to Britain, that Polk's administration would look favorably on a British proposal based around a division at the 49th parallel.[64] In June 1846, Pakenham presented an offer to the Polk administration, calling for a boundary line at the 49th parallel, with the exception that Britain would retain all of Vancouver Island, and British subjects would be granted limited navigation rights on the Columbia River until 1859.[65] Polk and most of his cabinet were prepared to accept the proposal, but Buchanan, in a reversal, urged that the United States seek control of all of the Oregon Territory.[66]

After winning the reluctant approval of Buchanan,[67] Polk submitted the full treaty to the Senate for ratification. The Senate ratified the Oregon Treaty in a 41–14 vote, with opposition coming from those who sought the full territory.[68] Polk's willingness to risk war with Britain had frightened many, but his tough negotiation tactics may have gained the United States concessions from the British (particularly regarding the Columbia River) that a more conciliatory president might not have won.[69]

The United States had been the first country to recognize Mexico's independence following the Mexican War of Independence, but relations between the two countries began to sour in the 1830s.[70] In the 1830s and 1840s, the United States, like France and Britain, sought a reparations treaty with Mexico for various acts committed by Mexican citizens and authorities, including the seizure of American ships.[70] Though the United States and Mexico had agreed to a joint board to settle the various claims prior to Polk's presidency, many Americans accused the Mexican government of acting in bad faith in settling the claims.[70] For its part, Mexico believed that the United States sought to acquire Mexican territory, and believed that many Americans filed specious or exaggerated claims.[70] The already-troubled Mexico–United States relations were further inflamed by the possibility of the annexation of Texas, as Mexico still viewed Texas as an integral part of their republic.[71] Additionally, Texas laid claim to all land north of the Rio Grande River, while Mexico argued that the more northern Nueces River was the proper Texan border.[72] Though the United States had a population more than twice as numerous and an economy thirteen times greater than that of Mexico, Mexico was not prepared to give up its claim to Texas, even if it meant war.[73]

The Mexican province of Alta California enjoyed a large degree of autonomy, and the central government neglected its defenses; a report from a French diplomat stated that "whatever nation chooses to send there a man-of-war and 200 men" could conquer California.[74] Polk placed great value in the acquisition of California, which represented new lands to settle as well as a potential gateway to trade in Asia.[75] He feared that the British or another European power would eventually establish control over California if it remained in Mexican hands.[76] In late 1845, Polk sent diplomat John Slidell to Mexico to win Mexico's acceptance of the Rio Grande border. Slidell was further authorized to purchase California for $20 million and New Mexico for $5 million.[77] Polk also sent Lieutenant Archibald H. Gillespie to California with orders to foment a pro-American rebellion that could be used to justify annexation of the territory.[78]

Following the Texan ratification of annexation in 1845, both Mexicans and Americans saw war as a likely possibility.[71] Polk began preparations for a potential war, sending an army led by General Zachary Taylor into Texas.[79] Taylor and Commodore David Conner of the U.S. Navy were both ordered to avoid provoking a war, but were authorized to respond to any Mexican breach of peace.[79] Though Mexican President José Joaquín de Herrera was open to negotiations, Slidell's ambassadorial credentials were refused by a Mexican council of government.[80] In December 1845, Herrera's government collapsed largely due to his willingness to negotiate with the United States; the possibility of the sale of large portions of Mexico aroused anger among both Mexican elites and the broader populace.[81]

As successful negotiations with the unstable Mexican government appeared unlikely, Secretary of War Marcy ordered General Taylor to advance to the Rio Grande River.[81] Polk began preparations to support a potential new government led by the exiled Mexican General Antonio López de Santa Anna with the hope that Santa Anna would sell parts of California.[82] Polk had been advised by Alejandro Atocha, an associate of Santa Anna, that only the threat of war would allow the Mexican government the leeway to sell parts of Mexico.[82] In March 1846, Slidell finally left Mexico after the government refused his demand to be formally received.[83] Slidell returned to Washington in May 1846, and gave his opinion that negotiations with the Mexican government were unlikely to be successful.[84] Polk regarded the treatment of his diplomat as an insult and an "ample cause of war", and he prepared to ask Congress for a declaration of war.[85]

Meanwhile, in late March 1846, General Taylor reached the Rio Grande, and his army camped across the river from Matamoros, Tamaulipas.[82] In April, after Mexican general Pedro de Ampudia demanded that Taylor return to the Nueces River, Taylor began a blockade of Matamoros.[84] A skirmish on the northern side of the Rio Grande ended in the death or capture of dozens of American soldiers, and became known as the Thornton Affair.[84] While the administration was in the process of asking for a declaration of war, Polk received word of the outbreak of hostilities on the Rio Grande.[84] In a message to Congress, Polk explained his decision to send Taylor to the Rio Grande, and stated that Mexico had invaded American territory by crossing the river.[86] Polk contended that a state of war already existed, and he asked Congress to grant him the power to bring the war to a close.[86] Polk's message was crafted to present the war as a just and necessary defense of the country against a neighbor that had long troubled the United States.[87] In his message, Polk noted that Slidell had gone to Mexico to negotiate a recognition of the Texas annexation, but did not mention that he also sought the purchase of California.[87]

Some Whigs, such as Abraham Lincoln, challenged Polk's version of events.[88] One Whig congressman declared "the river Nueces is the true western boundary of Texas. It is our own president who began this war. He has been carrying it on for months."[89] Nonetheless, the House overwhelmingly approved of a resolution authorizing the president to call up fifty thousand volunteers.[90] In the Senate, war opponents led by Calhoun also questioned Polk's version of events, but the House resolution passed the Senate in a 40–2 vote, marking the beginning of the Mexican–American War.[91] Many congressmen who were skeptical about the wisdom of going to war with Mexico feared that publicly opposing the war would cost them politically.[86][92]

Overview map of the war. Key:

Disputed territory   United States territory, 1848

Mexican territory retained after the Treaty of Guadalupe Hidalgo   Mexican territory lost in the Treaty of Guadalupe Hidalgo

In May 1846, Taylor led U.S. forces in the inconclusive Battle of Palo Alto, the first major battle of the war.[93] The next day, Taylor led the army to victory in the Battle of Resaca de la Palma, eliminating the possibility of a Mexican incursion into the United States.[93] Taylor's force moved south towards Monterrey, which served as the capital of the province of Nuevo León.[94] In the September 1846 Battle of Monterrey, Taylor defeated a Mexican force led by Ampudia, but allowed Ampudia's forces to withdraw, much to Polk's consternation.[95]

Meanwhile, Winfield Scott, the army's lone major general at the outbreak of the war, was offered the position of top commander in the war.[96] Polk, War Secretary Marcy, and Scott agreed on a strategy in which the US would capture northern Mexico and then pursue a favorable peace settlement.[96] However, Polk and Scott experienced mutual distrust from the beginning of their relationship, in part due to Scott's Whig affiliation and former rivalry with Andrew Jackson.[97] Additionally, Polk sought to ensure that both Whigs and Democrats would serve in important positions in the war, and was offended when Scott suggested otherwise; Scott also angered Polk by opposing Polk's effort to increase the number of generals.[98] Having been alienated from Scott, Polk ordered Scott to remain in Washington, leaving Taylor in command of Mexican operations.[93] Polk also ordered Commodore Conner to allow Santa Anna to return to Mexico from his exile, and sent an army expedition led by Stephen W. Kearny towards Santa Fe.[99]

While Taylor fought the Mexican army in east, U.S. forces took control of California and New Mexico.[100] Army Captain John C. Frémont led settlers in Northern California in an attack on the Mexican garrison in Sonoma, beginning the Bear Flag Revolt.[101] In August 1846, American forces under Kearny captured Santa Fe, capital of the province of New Mexico.[102] He captured Santa Fe without firing a shot, as the Mexican Governor, Manuel Armijo, fled from the province.[103] After establishing a provisional government in New Mexico, Kearny took a force west to aid in the conquest of California. After Kearny's departure, Mexicans and Puebloans rebelled against the provisional government in the Taos Revolt, but U.S. forces crushed the uprising.[104] At roughly the same time that Kearny captured Santa Fe, Commodore Robert F. Stockton landed in Los Angeles and proclaimed the capture of California.[102] Californios rose up in rebellion against U.S. occupation, but Stockton and Kearny suppressed the revolt with a victory in the Battle of La Mesa. After the battle, Kearny and Frémont became embroiled in a dispute over the establishment of a government in California.[105] The controversy between Frémont and Kearny led to a break between Polk and the powerful Missouri Senator Thomas Hart Benton, who was the father-in-law of Frémont.[106]

Whig opposition to the war grew after 1845, while some Democrats lost their initial enthusiasm.[107] In August 1846, Polk asked Congress to appropriate $2 million in hopes of using that money as a down payment for the purchase of California in a treaty with Mexico.[108] Polk's request ignited opposition to the war, as Polk had never before made public his desire to annex parts of Mexico (aside from lands claimed by Texas).[108] A freshman Democratic Congressman, David Wilmot of Pennsylvania, offered an amendment known as the Wilmot Proviso that would ban slavery in any newly acquired lands.[109] The appropriations bill, including the Wilmot Proviso, passed the House with the support Northern Whigs and Northern Democrats, breaking the normal pattern of partisan division in congressional votes. Wilmot himself held anti-slavery views, but many pro-slavery Northern Democrats voted for the bill out of anger at Polk's perceived bias towards the South. The partition of Oregon, the debate over the tariff, and Van Buren's antagonism towards Polk all contributed to Northern anger. The appropriations bill, including the ban on slavery, was defeated in the Senate, but the Wilmot Proviso injected the slavery debate into national politics.[110]

Polk's Democrats would pay a price for the resistance to the war and the growing issue of slavery, as Democrats lost control of the House in the 1846 elections. However, in early 1847, Polk was successful in passing a bill raising further regiments, and he also finally won approval for the money he wanted to use for the purchase of California.[111]

Santa Anna returned to Mexico City in September 1846, declaring that he would fight against the Americans.[112] With the duplicity of Santa Anna now clear, and with the Mexicans declining his peace offers, Polk ordered an American landing in Veracruz, the most important Mexican port on the Gulf of Mexico.[112] As a march from Monterrey to Mexico City was implausible due to rough terrain,[113] Polk had decided that a force would land in Veracruz and then march on Mexico City.[114] Taylor was ordered to remain near Monterrey, while Polk reluctantly chose Winfield Scott to lead the attack on Veracruz.[115] Though Polk continued to distrust Scott, Marcy and the other cabinet members prevailed on Polk to select the army's most senior general for the command.[116]

In March 1847, Polk learned that Taylor had ignored orders and had continued to march south, capturing the northern Mexican town of Saltillo.[117] Taylor's army had repulsed a larger Mexican force, led by Santa Anna, in the February 1847 Battle of Buena Vista.[117] Taylor won acclaim for the result of the battle, but the theater remained inconclusive.[117] Rather than pursuing Santa Anna's forces, Taylor withdrew back to Monterrey.[118] Meanwhile, Scott landed in Veracruz and quickly won control of the city.[119] Following the capture of Veracruz, Polk dispatched Nicholas Trist, Buchanan's chief clerk, to negotiate a peace treaty with Mexican leaders.[119] Trist was ordered to seek the cession of Alta California, New Mexico, and Baja California, recognition of the Rio Grande as the southern border of Texas, and American access across the Isthmus of Tehuantepec.[120]

In April 1847, Scott defeated a Mexican force led by Santa Anna at the Battle of Cerro Gordo, clearing the way for a march on Mexico City.[121] In August, Scott defeated Santa Anna again at the Battle of Contreras and the Battle of Churubusco.[122] With these victories over a larger force, Scott's army was positioned to besiege Mexico's capital.[122] Santa Anna negotiated a truce with Scott, and the Mexican foreign minister notified Trist that they were ready to begin negotiations to end the war.[123] However, the Mexican and American delegations remained far apart on terms; Mexico was only willing to yield portions of Alta California, and still refused to agree to the Rio Grande border.[124] While negotiations continued, Scott captured the Mexican capital in the Battle for Mexico City.[125]

In the United States, a heated political debate emerged regarding how much of Mexico the United States should seek to annex, with Whigs such as Henry Clay arguing that the United States should only seek to settle the Texas border question, and some expansionists arguing for the annexation of all of Mexico.[126] Frustrated by the lack of progress in negotiations, and troubled by rumors that Trist was willing to negotiate on the Rio Grande border, Polk ordered Trist to return to Washington.[127] Polk decided to occupy large portions of Mexico and wait for a Mexican peace offer.[128] In late 1847, Polk learned that Scott had court-martialed a close ally of Polk's, Gideon Johnson Pillow.[129] Outraged by that event, Polk demanded Scott's return to Washington, with William Orlando Butler tapped as his replacement.[129]

The Mexican Cession (in red) was acquired through the Treaty of Guadalupe Hidalgo. The Gadsden Purchase (in orange) was acquired through purchase after Polk left office.

In September 1847, Manuel de la Peña y Peña replaced Santa Anna as President of Mexico, and Pena and his Moderado allies showed a willingness to negotiate based on the terms Polk had relayed to Trist.[130] In November 1847, Trist received Polk's order to return to Washington.[130] After a period of indecision, and with the backing of Scott and the Mexican government (which was aware that Polk had ordered Trist's recall), Trist decided to enter into negotiations with the Mexican government.[130] As Polk had made no plans to send an envoy to replace him, Trist thought that he could not pass up the opportunity to end the war on favorable terms.[130] Though Polk was outraged by Trist's decision, he decided to allow Trist some time to negotiate a treaty.[131]

Throughout January 1848, Trist regularly met with Mexican officials in Guadalupe Hidalgo, a small town north of Mexico City.[132] Trist was willing to allow Mexico to keep Lower California, but successfully haggled for the inclusion of the important harbor of San Diego in a cession of Upper California.[132] The Mexican delegation agreed to recognize the Rio Grande border, while Trist agreed to have the United States cover prior American claims against the Mexican government.[132] The two sides also agreed to the right of Mexicans in annexed territory to leave or become U.S. citizens, American responsibility to prevent cross-border Indian raids, protection of church property, and a $15 million payment to Mexico.[132] On February 2, 1848, Trist and the Mexican delegation signed the Treaty of Guadalupe Hidalgo.[132]

Polk received the document on February 19,[133][134] and, after the Cabinet met on the 20th, decided he had no choice but to accept it. If he turned it down, with the House by then controlled by the Whigs, there was no assurance Congress would vote funding to continue the war. Both Buchanan and Walker dissented, wanting more land from Mexico.[135] Some senators opposed the treaty because they wanted to take no Mexican territory; others hesitated because of the irregular nature of Trist's negotiations. Polk waited in suspense for two weeks as the Senate considered it, sometimes hearing that it would likely be defeated, and that Buchanan and Walker were working against it. On March 10, the Senate ratified the treaty in a 38–14 vote that cut across partisan and geographic lines.[136] The Senate made some modifications to treaty, and Polk worried that the Mexican government would reject the new terms. Despite those fears, on June 7, Polk learned that Mexico had ratified the treaty.[137] Polk declared the treaty in effect as of July 4, 1848, thus ending the war.[138]

The Mexican Cession added 600,000 square miles of territory to the United States, including a long Pacific coastline.[137] The treaty also recognized the annexation of Texas and acknowledged American control over the disputed territory between the Nueces River and the Rio Grande. Mexico, in turn, received $15 million.[132] The war had cost the lives of nearly 14,000 Americans and 25,000 Mexicans, and had cost the United States roughly one hundred million dollars.[137][139] With the exception of the territory acquired by the 1853 Gadsden Purchase, the territorial acquisitions under Polk established the modern borders of the Contiguous United States.[138]

United States states and territories when Polk entered office

United States states and territories when Polk left office

Polk had been anxious to establish a territorial government for Oregon once the treaty was effective in 1846, but the matter became embroiled in the arguments over slavery, though few thought Oregon suitable for that institution. A bill to establish an Oregon territorial government passed the House after being amended to bar slavery; the bill died in the Senate when opponents ran out the clock on the congressional session. A resurrected bill, still barring slavery, again passed the House in January 1847, but it was not considered by the Senate before Congress adjourned in March. By the time Congress met again in December, California and New Mexico were in U.S. hands, and Polk in his annual message urged the establishment of territorial governments in California, New Mexico, and Oregon.[140] The Missouri Compromise had settled the issue of the geographic reach of slavery within the Louisiana Purchase territories by prohibiting slavery in states north of 36°30′ latitude. Polk sought to extend this line into the newly acquired territory.[141] If extended to the Pacific, this would have made slavery illegal in Northern California, but would have allowed it in Southern California.[142] A plan to accomplish the extension was defeated in the House by a bipartisan alliance of Northerners.[143] As the last congressional session before the 1848 election came to a close, Polk signed the lone territorial bill passed by Congress, which established the Territory of Oregon and prohibited slavery in it.[144]

When Congress reconvened in December 1848, Polk again called for the establishment territorial governments in California and New Mexico, a task made especially urgent by the onset of the California Gold Rush.[145] However, the divisive issue of slavery blocked any such legislation. Polk made it clear that he would veto a territorial bill that would have had the laws Mexico apply to the southwest territories until Congress, considering it to be the Wilmot Proviso in another guise. It was not until the Compromise of 1850 that the matter of the territories was resolved.[146]

Polk's ambassador to the Republic of New Granada, Benjamin Alden Bidlack, negotiated the Mallarino–Bidlack Treaty with the government of New Granada in 1846.[147] Though Bidlack had initially only sought to remove tariffs on American goods, Bidlack and New Granadan Foreign Minister Manuel María Mallarino negotiated a broader agreement that deepened military and trade ties between the two countries.[147] The treaty also allowed for the construction of the Panama Railway.[148] In an era of slow overland travel, the treaty gave the United States a route to more rapidly travel between its eastern and western coasts.[148] In exchange, Bidlack agreed to have the United States guarantee New Granada's sovereignty over the Isthmus of Panama.[147] The treaty won ratification in both countries in 1848.[148] The agreement helped to establish a stronger American influence in the region, as the Polk administration sought to ensure that Great Britain would not dominate Central America.[148] The United States would use the Mallarino-Bidlack Treaty as justification for numerous military interventions in Panama.[147]

In mid-1848, President Polk authorized his ambassador to Spain, Romulus Mitchell Saunders, to negotiate the purchase of Cuba and offer Spain up to $100 million, an astounding sum at the time for one territory, equal to $3.38 billion in present-day terms.[149] Cuba was close to the United States and had slavery, so the idea appealed to Southerners but was unwelcome in the North. However, Spain was still making huge profits in Cuba (notably in sugar, molasses, rum, and tobacco), and thus the Spanish government rejected Saunders' overtures.[150] Though Polk was eager to acquire Cuba, he refused to support the proposed filibuster expedition of Narciso López, who sought to invade and annex Cuba.[151]

The Tariff of 1842 had set relatively high tariff rates, and Polk made a reduction of tariff rates the top priority of his domestic agenda.[152] Though he had taken an ambivalent position on the tariff during the 1844 campaign in order to win Northern votes, Polk had long opposed a high tariff.[153] Many Americans, especially in the North, favored high tariffs as a means of protecting domestic manufacturing from foreign competition. Polk believed that protective tariffs were unfair to other economic activities, and he favored reducing tariff rates to the minimum level necessary for funding the federal government.[152] Upon taking office, Polk directed Secretary of the Treasury Walker to draft a law that would lower tariff rates.[153] Though foreign policy and other issues prevented Congress and the administration from focusing on tariff reduction in 1845 and early 1846, Walker worked with Congressman James Iver McKay to develop a tariff reduction bill. In April 1846, McKay reported the bill out of the House Ways and Means Committee for consideration by the full House of Representatives.[154]

After intense lobbying by both sides, the bill passed the House on July 3, with the vast majority of favorable votes coming from Democrats.[155] Consideration then moved to the Senate, and Polk intensely lobbied a group of wavering senators to assure passage of the bill.[156] In a close vote that required Vice President Dallas to break a tie, the Senate approved the tariff bill in July 1846.[157] Dallas, from protectionist Pennsylvania, voted for the bill because he decided that his best political prospects lay in supporting the administration.[158] Following the congressional passage of the bill, Polk signed the Walker Tariff into law, substantially reducing the rates that had been set by the Tariff of 1842.[154] The Walker Tariff would remain in place until the passage of the Tariff of 1857, staying in effect longer than any other tariff measure of the nineteenth century.[159] The reduction of tariffs in the United States and the repeal of the Corn Laws in Great Britain led to a boom in Anglo-American trade[160] and, in large part due to growing international trade, the economy entered a strong period of growth in the late 1840s.[161]

In his inaugural address, Polk called upon Congress to re-establish the Independent Treasury System under which government funds were held in the Treasury and not in banks or other financial institutions.[162] Under that system, the government would store federal funds in vaults in the Treasury Building and other government buildings, where those funds would remain until they were used to fund the government.[163] President Van Buren had previously established the Independent Treasury system, but it had been abolished during the Tyler administration.[164] Under the status quo that prevailed when Polk took office, the government deposited its funds in state banks, which could then use those funds in ordinary banking operations. Polk believed that this policy resulted in inflation, and was also philosophically opposed to involving the government in banking.[165] The Whigs had wanted to create a new national bank since the expiration of the charter of the Second Bank of the United States in 1836, but their efforts had been vetoed by President Tyler, and Polk strongly opposed the re-establishment of a national bank.[165] In a party-line vote, the House of Representatives approved Polk's Independent Treasury bill in April 1846.[163] After personally winning the support of Senator Dixon Lewis, the chairman of the Senate Finance Committee, Polk was able to push the Independent Treasury Act through the Senate, and he signed the act into law on August 6, 1846. The system would remain in place until the passage of the Federal Reserve Act in 1913.[160]

During Polk's presidency, Congress passed bills to provide federal funding for internal improvements such as roads, canals, and harbors. Those who favored such funding, many of whom were Whigs, believed that internal improvements aided economic development and Western settlement. Unlike tariffs and monetary policy, support for federally-funded internal improvements split the Democratic Party, and a coalition of Democrats and Whigs arranged for the passage of internal improvement bills despite Polk's opposition.[166] Polk considered internal improvements to be matters for the states, and feared that the passage of federal internal improvements bill would encourage legislators to compete for favors for their home district; Polk felt that such competition for federal resources damaged the virtue of the republic. When Congress passed the Rivers and Harbors Bill in 1846 to provide $500,000 to improve port facilities, Polk vetoed it. Polk believed that the bill was unconstitutional because it unfairly favored particular areas, including ports that had no foreign trade.[167] In this regard he followed his hero Jackson, who had vetoed the Maysville Road Bill in 1830 on similar grounds.[168] In 1847, Polk pocket vetoed another internal improvements bill, and Congress would not pass a similar bill during his presidency.[169]

Like Jackson, Polk saw slavery as a side issue compared to other matters such as territorial expansion and economic policy.[170] However, the issue of slavery became increasingly polarizing during the 1840s, and Polk's expansionary policies increased its divisiveness.[170] During his presidency, many abolitionists harshly criticized him as an instrument of the "Slave Power", and claimed that he supported western expansion because he wanted to extend slavery into new territories.[171] For his part, Polk accused both northern and southern leaders of attempting to use the slavery issue for political gain.[172] The divisive debate over slavery in the territories led to the creation of the Free Soil Party, an anti-slavery (though not abolitionist) party that attracted Democrats, Whigs, and members of the Liberty Party.[173]

The California Gold Rush began under Polk.

Authoritative word of the discovery of gold in California did not arrive in Washington until after the 1848 election, by which time Polk was a lame duck. Polk was delighted by the discovery of gold, seeing it as validation of his stance on expansion, and he referred to the discovery several times in his final annual message to Congress that December. Shortly thereafter, actual samples of the California gold arrived, and Polk sent a special message to Congress on the subject. The message, confirming less authoritative reports, caused large numbers of people to move to California, both from the U.S. and abroad, thus helping to spark the California Gold Rush.[174] The California gold rush injected large quantities of gold into the U.S. economy, helping to ease a long-term shortage of gold coins. In large because of this gold, the Whigs were unable to whip up popular enthusiasm for a revival of the national bank after Polk left office.[175]

In response to the Gold Rush, the House introduced the Coinage Act of 1849 which allowed for the minting of two new denominations of gold coins, the gold dollar and the gold $20 or double eagle. It further defined the variances which were permissible in United States gold coinage. The act was approved on March 3, 1849, and Polk signed it on that same day, marking one of his final acts as president. The act contains four sections.

One of Polk's last acts as president was to sign the bill creating the Department of the Interior (March 3, 1849). This was the first new cabinet position created since the early days of the Republic. Polk had misgivings about the federal government usurping power over public lands from the states. Nevertheless, the delivery of the legislation on his last full day in office gave him no time to find constitutional grounds for a veto, or to draft a sufficient veto message, so he signed the bill.[176]

Three states were admitted to the Union during Polk's presidency:

• Texas – December 29, 1845
• Iowa – December 28, 1846
• Wisconsin – May 29, 1848

• Notaro, Carmen. “Biography and James K. Polk: Observations on an Historiography Spanning Two Centuries.” Tennessee Historical Quarterly 75#4 (2016), pp. 260–75, online.