The promise of America has always been the promise of a new start. And that promise became one of territorial expansion the moment Americans began to head west past the bounds of the Mississippi. “From sea to shining sea,” the famous line from the song “America, the Beautiful,” quickly became one of the guiding ideals of American life; that is, ordinary, every-day Americans would not, and could not, rest until the United States stretched from the Atlantic to the Pacific. And although he was not the first to put his eyes on the territory west of the Louisiana Purchase, it was the presidency of James K. Polk (1845-1849) that put the finishing touches on the last major acquisition of new territory before the Civil War. A member of the Jacksonian-nationalist wing of the Democratic Party, Polk’s intentions were clear from the start—his famous campaign slogan, “54-40 or Fight!” indicated his intention to settle the status of the Oregon Territory with Great Britain on American terms. But even more famously associated with Polk is the Mexican-American War, and with it the acquisition of New Mexico and Upper California.
During the administration of John Tyler (1841-1845), the independent nation of Texas and the United States Congress began moving towards Texan annexation. (Texas, a province of Mexico, had achieved its independence in 1836 after a year-long war against the central authorities.) Although not formally completed until Polk’s presidency, this action on the part of the United States brought strong condemnations from Mexico, which had only recently recognized Texas as an independent nation. Indeed, Mexico had recognized Texas on the condition that Texas would not pursue annexation with the United States. The border between Texas and Mexico also remained unsettled, a dispute that the United States would inherit once Texas joined the Union.
Upon the news that the United States was in the final stages of annexation (it still needed to be approved by the people of Texas), Mexico cut off all official diplomatic ties with Washington. Many Mexicans believed that the Texan Revolution was ultimately a shameless land grab by the United States, and that more threats to Mexican territory were on the way. From the perspective of the United States, the end of all diplomatic contact with Mexico was just another addition to an already existing list of grievances. For many years, Americans in Mexico had dealt with what they regarded as corrupt Mexican officials. According to complaints lodged with the U.S. government, some of these officials kidnapped American citizens, others laid claim to American ships and cargoes lying in Mexican harbors, and still others killed Americans. In 1839, the United States and Mexico agreed to form a joint commission to gather the information related to these claims, and then submit them to an arbitrator who would determine how much money should be paid to American citizens affected by these abuses. Once the information had been collected, the arbitrator determined Americans were owed about $2 million, payable in installments. A financially drained Mexico was ultimately unable to pay most of the installments, and by the time diplomatic ties were cut it had stopped payments altogether.
In September of 1845, William S. Parrot, a confidential agent sent to Mexico by Polk, reported that Mexico was interested in reopening negotiations over the Texas issue, including the matter of boundaries. A month later, Consul General John Black in Mexico City, upon receiving instructions from Secretary of State James Buchanan to see if the Mexicans were interested in opening up diplomatic contacts, confirmed that the Mexicans were interested in dealing with the problem of Texas. Polk took the opportunity to send Louisianan John Slidell (who later, famously, was sent to Europe on behalf of the Confederacy) with the powers of a full envoy extraordinary and minister plenipotentiary to Mexico. His mission was initially to be kept a secret, not only because of fears that the British or French might thwart it, but also because it was decided early on (September 16, 1845) that one of its great objects, in addition to settling the issues of Texas and American financial claims, was “to adjust a permanent boundary between Mexico and the United States, and that in doing this the Minister would be instructed to purchase for a pecuniary consideration Upper California and New Mexico.” Mexican authorities refused to negotiate with Slidell on this comprehensive basis, arguing that they had only agreed to consider resolution of the issue of Texas.
Polk’s ambitions to obtain new territory from Mexico also created a complex domestic political problem for the Democratic president, because many members of the opposition Whig Party were against territorial expansion, especially to the south, because they believed that such expansion ultimately meant the expansion of slavery. In addition, some northern Democrats and Whigs wanted to focus on protecting American claims to the undeniably free soil of Oregon. And a few Southern slaveholders, notably John C. Calhoun, were suspicious of Polk’s plans, but for different reasons. They feared that further attempts to expand beyond Texas, particularly if it involved war with Mexico, would provide a vehicle to strengthen the federal government and unite the opponents of slavery (as exemplified later by the anti-slavery Wilmot Proviso, which gained the support of many northern Democrats).
At the same time, Polk was negotiating with Great Britain over the status of the Oregon Territory. For some time American and British diplomats had been discussing possible solutions for the boundary between the two nations in Oregon. Americans had been traveling to and settling in the Oregon Territory (what is now present day Oregon, Washington, Idaho, and British Columbia) since at least the 1830s, and the United States and Great Britain had treaty agreements going back to 1818 to occupy the territory, in a joint manner. Britain’s chief interest in the territory came from the fur trapping activities of the Hudson’s Bay Company; however, as the number of beavers declined and the number of American immigrants increased, its interest in the area began to wane while American interest began to rise. Negotiations focused on where, exactly, a boundary could be drawn. Polk was chiefly interested in negotiating a boundary that gave the United States access to a Pacific port and, despite the campaign slogan, was prepared to compromise well short of the line of maximum American claims (54 degrees, 40 minutes). Ultimately, in the Oregon Treaty of 1846, this boundary was drawn at the 49th parallel, curving south so that Vancouver Island would remain entirely British territory. Polk was able to time the negotiations such that the compromise over Oregon had essentially been reached before the final crisis with Mexico, thus freeing him to turn American attention to the south, while muting later domestic criticism by northern expansionists that he had conceded too much over Oregon.
In any case, there were some rumors at the time that the British and the French were also interested in claiming California from Mexico (see Polk’s Diary entry for October 24, 1845 in which he, in conversation with Thomas Hart Benton, remarked that Britain has its eye on California), and Polk intended to head them off so that the United States could truly go from “sea-to-shining-sea.” Direct access to the Pacific Ocean held immense benefits for the United States, and Polk was determined to obtain those benefits. Although possession of the Oregon Territory gave the United States some Pacific access, the best ports were located within Mexican territory. Thus, Polk instructed Slidell very clearly to obtain Upper California and New Mexico if possible—even providing him the ability to adjust the amount of money offered if the Mexicans refused the first offer. Additionally, Polk sent famous explorer John C. Frémont to “map out” California, an obvious ploy on Polk’s part to jump start the territorial acquisition of Upper California.
In June of 1845, Polk expressed fears that Mexico would invade the disputed territory on the border with Mexico, between the Nueces River and the Rio Grande, so he proceeded to station General Zachary Taylor and about 3000 soldiers right at the edge of that territory. After Slidell arrived in Mexico, Taylor, in response to orders from the War Department, moved his forces up to the Rio Grande – the river which Polk claimed was the actual boundary of Texas and Mexico. Here Taylor remained, across the river from the Mexican city of Matamoros, ignoring repeated warnings from the Mexicans to leave. Mexican forces crossed the river and attacked an American patrol in late April of 1846. We cannot say for certain whether Polk meant to provoke war by ordering Taylor up to the Rio Grande, or whether this represented an attempt to coerce the Mexicans into accepting American terms; but many at the time argued this action at least contributed to the outbreak of an unnecessary conflict.
In any case, for the several months prior to this event, Polk had declared his intention to take “strong measures” against Mexico, whatever that might have meant. Repeatedly, Polk wrote in his diary of the necessity to redress the grievances between the United States and the country on its southern border. On February 17, Polk told his cabinet “that it would be necessary to take strong measures towards Mexico before our difficulties with that Government could be settled” and furthermore that if John Slidell was refused as minister again, he would ask Congress “to confer authority on the executive to take redress into our own hands by aggressive measures.” There are no statements like this on Mexico in Polk’s diary again until April—but the fact is that some sort of decisive action was clearly on Polk’s mind for months before the actual clash between soldiers at the Rio Grande.
On April 7, in another cabinet meeting, Polk suggested that if Slidell was not accredited by Mexico, he would “make a communication to Congress recommending that Legislative measures be adopted, to take the remedy for the injuries and wrongs we had suffered into our own hands.” On April 18, in a conversation with Calhoun, Polk remarked that “our relations with Mexico had reached a point where we could not stand still but must assert our rights firmly; that we must treat all nations whether weak or strong alike, and that I saw no alternative but strong measures towards Mexico.” On April 21, Polk told his cabinet that the status quo with Mexico must soon change and that a description of their relations should be brought before Congress “accompanied with a message strongly and decidedly recommending that strong measures be adopted to take the redress of our complaints against that government into our own hands.” At a cabinet meeting on April 25, Polk stated:
…That I thought it was my duty to make a communication to Congress on the subject without unnecessary delay. I expressed my opinion that we must take redress for the injuries done us into our own hands, that we had attempted to conciliate Mexico in vain, and had forborne until forbearance was no longer either a virtue or patriotic; and that in my opinion we must treat all nations, whether great or small, strong or weak, alike, and that we should take a bold and firm course towards Mexico.
Again, on April 28 the Cabinet agreed that a message should be sent to Congress laying the subject of Mexico before it and recommending that measures be adopted for redress.
In a May 3rd conversation with Senator Thomas Hart Benton, Polk expressed his desire of submitting a message to Congress soon on the subject of Mexico. On May 8, Slidell arrived in Washington and briefed the President on the latest developments. On May 9, Polk and his cabinet resolved to send a message to Congress by the end of the next week, asking for a declaration of war. News reached Polk early that evening from General Taylor on the clash that occurred between his soldiers and those of Mexico several days before. In Polk’s mind, national honor, not just interest, was now at stake, as Americans had been attacked without provocation and American blood had been shed. The case for war was now politically stronger than it otherwise would have been. Polk immediately got to work on a message, which he sent to Congress the following Monday, May 11.
Polk’s War Message to Congress was fairly straightforward. While Polk neglected to list all of the grievances that existed between Mexico and the United States, he did refer the Members back to his first Annual Message (State of the Union Address) that past December, which detailed those complaints. Polk does mention that Mexico abrogated her agreements to pay the claims of American citizens—and that “a government either unable or unwilling to enforce the execution of such treaties fails to perform one of its plainest duties”— but he mainly addresses events that had taken place between his Annual Message and the special Message he was now submitting to Congress.
The first wrong detailed in Polk’s Message was Mexico’s refusal to accept John Slidell as minister. Polk described this as an outrageous thing for Mexico to do because, according to him, Mexico had asked for a minister “entrusted with full powers to adjust all the questions in dispute between the two governments.” In Polk’s telling, he had sent Slidell in response to Mexico’s entreaties as full envoy extraordinary and minister plenipotentiary. For Polk, the refusal to accept Slidell was representative of Mexico abrogating its duties; he claims that Mexican authorities were “solemnly pledged by official acts … to receive and accredit an American envoy” and that “the indignity of its rejection was enhanced by the manifest breach of faith in refusing to admit the envoy who came because they had bound themselves to receive him.” He expresses disbelief that Mexico would not accept a minister from the United States for four reasons—(1) because they asked for a minister to be sent, (2) because Slidell “had full powers to adjust every question of difference”, (3) because the United States was anything but unreasonable in its propositions, and (4) because Mexico herself has not offered any propositions (and so there has been no opportunity for the United States to reject her ideas).
Although there might have been some confusion or misunderstanding within Polk’s administration about what kind of envoy the Mexicans wanted the United States to send to treat with them, Polk insists in his Message that sending a full minister was the only thing that he could do, because “the redress of the wrongs of our citizens naturally and inseparably blended itself with the question of boundary.” In Polk’s mind, “the settlement of the one question in any correct view of the subject involves that of the other. I could not for a moment entertain the idea that the claims of our much-injured and long-suffering citizens, many of which had existed for more than twenty years, should be postponed or separated from the settlement of the boundary question.”
Left unmentioned to Congress were Polk’s designs on purchasing New Mexico and Upper California. Slidell had to be sent as a full minister in order to negotiate for those territories—but Polk also may have calculated that sending Slidell as a full minister would not be acceptable to Mexico, which would provide a pretense for the United States to initiate a war with Mexico for that territory, if Mexico did not start the war itself. Or this may have been another gambit in Polk’s strategy of coercive diplomacy, with war as a fallback option if Mexico proved intransigent, which proved to be the case. Luckily for Polk, in political terms, Mexico did make the “first move” by attacking and capturing a detachment of Taylor’s soldiers.
At this point in the Message, Polk defends his placement of troops between the Rio Grande and Nueces rivers because of a “threatened invasion,” due to the annexation of Texas by the United States. Polk says that Texas (and thus the United States following annexation) claimed all the land to the Rio Grande—jurisdiction and revenue collection had both been exercised by Texan and American officials in that area, Polk asserts. This, along with a number of other considerations, led Polk to command troops to protect the area in order to prevent the “threatened invasion.”
Furthermore, Polk tells Congress, he gave very specific instructions to General Taylor to “abstain from all aggressive acts toward Mexico or Mexican citizens and to regard the relations between that Republic and the United States as peaceful unless she should declare war or commit acts of hostility indicative of a state of war. He was specially directed to protect private property and respect personal rights.” Polk thus absolves himself and Taylor from any responsibility for the actions that Mexico took. The United States was merely exercising jurisdiction in land that it claimed to control, and Taylor was merely positioning himself to protect that claim. Polk does not acknowledge that there were Mexican citizens living within the disputed territory, nor that it was disputed in the first place—a point that Abraham Lincoln, in an 1848 speech to the House, brings to the fore when attempting to determine the true causes of the war.
At the end of the Message, Polk wonders whether or not the United States could have prevented the clash at the Rio Grande by acting sooner and more forcefully, especially with the amount of commerce that had previously taken place between the two countries. Instead, the United States’ “forbearance has gone to such an extreme as to be mistaken in its character.” By the spring of 1846, the possibility of negotiation or solving the problem before bloodshed had passed because “the cup of forbearance had been exhausted” and, finally, after “reiterated menaces, Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil. She has proclaimed that hostilities have commenced, and that the two nations are now at war.”
Polk concludes his Message by asking Congress to declare war on Mexico. Since “war exists, and, notwithstanding all our efforts to avoid it, exists by the act of Mexico herself, we are called upon by every consideration of duty and patriotism to vindicate with decision the honor, the rights, and the interests of our country,” the United States had no choice but to respond in kind. Polk asks Congress for authority to call up volunteers for no less than six to twelve months, and for money to provide to those soldiers. Polk ends with his wish to “not only terminate hostilities speedily, but to bring all matters in dispute between this Government and Mexico to an early and amicable adjustment” and to renew negotiations with Mexico whenever she is ready to make or receive propositions of her own. He does not lay out specific war aims for the United States, or indicate whether American diplomatic objectives might be expanded due to Mexican intransigence (e.g., through financial or territorial indemnities). Nor does he suggest a strategy designed to achieve his war aims. Polk clearly expected that the war would result in a quick and decisive victory.
On May 12, 1846, Congress voted to approve a declaration of war against Mexico, or, literally, a declaration that a state of war now existed. This declaration was cleverly attached as a preamble to a bill appropriating $10 million for the support of American troops and authorizing the president to raise fifty thousand men for the defense of American territory. The amendment attaching the preamble to the appropriations bill passed in the House by a vote of 123-67 (which indicated the strength of opposition to the war, primarily by the Whigs). A test vote in the Senate passed even more narrowly, 26-20. But the final legislative package was such that the Whigs were now in a position that a “no” vote on the appropriations bill would leave them open to charges that they had failed to support American troops under fire. The official tally for war was 173-14 in the House, with 35 abstentions, including 22 Democrats (former President John Quincy Adams was one of those fourteen to vote against the bill). The Senate concurred, 40-2, with 3 abstentions, including Calhoun. On May 13, the President issued a proclamation announcing the state of war.
 For a map of Upper California and New Mexico (referenced here and later) see: http://wchsutah.org/maps/upper-california-1847.jpg
 There seems to have been some confusion on the American side about what, exactly, the Mexicans were requesting in the first place. Was it a minister to discuss all points of contention between the two nations, or a negotiator merely there to resolve the issue of Texas? For a discussion of the confusion, see David Pletcher, The Diplomacy of Annexation (278). The official Mexican position was that they refused to accept Slidell as a minister, not because they did not want to negotiate some of their problems with the United States, but because Mexico never asked for a minister with full powers—this would imply that diplomatic relations between the two countries were back to normal, something that Mexico was not admitting by asking for a negotiator. Rather, Mexico merely asked for someone who could negotiate with them over the Texas question and boundary issues. Additionally, the political situation in Mexico prevented the government of General Herrara, in power when Slidell arrived, from even meeting with a full minister from the United States without popular backlash (ultimately, General Herrara’s government was replaced with the government of General Paredes soon after Slidell’s arrival). Slidell tried again after the ascension of General Paredes and was still rejected from taking his post—again because the political situation in Mexico prevented the Mexican government from accepting a minister provided with full powers from the United States. Return to text
 In this light, we should note the adamant refusal of Polk in the days following his May 1846 War Message to Congress to say anything in the diplomatic dispatches about war to Britain and France about Upper California and New Mexico, despite Buchanan’s wish to assure them that the United States did not intend to take those territories in the war with Mexico. Return to text
 See, for instance, Polk’s diary entry of August 26, 1845, in which the cabinet briefly discussed “the proper means of defending that territory against the threatened invasion of Mexico” and the entry for August 29, 1845 in which Polk described the orders provided to Taylor in case of invasion. Return to text
 Texas had laid claim to the Rio Grande as its southern boundary and had been actively working since at least 1839 to get Mexican recognition of such a boundary. For more information about Texas’s claims, see The Diplomacy of Annexation (76-79). For Polk’s attitude that Texas should be protected along its Rio Grande border, see above (253-254). For a map of the land that Texas claimed see: http://www.lib.utexas.edu/maps/atlas_texas/texas_land_grants.jpg.
 Polk’s strategy to acquire territory from Mexico included a third option, besides purchase (through coercion) and war – a “spontaneous” revolution in California, which would detach that province from Mexican rule. The new republic of California would then apply for admission into the Union. Return to text
For Further Reading
Polk’s War Message to Congress (May 11, 1846).
Polk’s instructions to Slidell: http://babel.hathitrust.org/cgi/pt?id=mdp.39015074697312;view=1up;seq=224
Lincoln’s speech to Congress in 1848 (briefly mentioned above): http://www.animatedatlas.com/mexwar/lincoln2.html
Howe, Daniel Walker. What Hath God Wrought: The Transformation of America, 1815-1848. Oxford: Oxford University Press, 2007.
Merk, Frederick. Manifest Destiny and Mission in American History: A Reinterpretation. Boston: Harvard University Press, 1995.
Merry, Robert W. A Country of Vast Designs. New York: Simon & Schuster, 2009.
Pletcher, David M. The Diplomacy of Annexation: Texas, Oregon, and the Mexican War. Columbia: The University of Missouri Press, 1973.