In justifying the validity of President James K. Polk’s decision to go to War with Mexico several issues must be examined. 1) Was the decision to go to war predetermined? 2) Was the boundary of Texas the Rio Grande River, as proclaimed by President Polk? 3) Did slavery play a part in the decision to go to war? 4) Did Mexico provoke the war by refusing to negotiate with American diplomats?

The Treaty of Guadalupe-Hidalgo was signed on February 2, 1848 ceding Texas with the Rio Grande boundary, New Mexico, and California. The outcome of this war enabled President James K. Polk to realize his dream of geographic expansion and Manifest Destiny. But this war was not without its controversy and raises questions of the wars justification.

On April 26, 1846, sixty-three dragoons, commanded by Captain Seth B. Thorton, had been ambushed by Mexican cavalry. The news reached the White House on May 9, 1846 (Dufour, 1968 page 11). Polk's followers jubilantly proclaimed that American blood has been shed on American soil! Why were his followers so jubilant that American blood had been shed? Was this war predetermined? Perhaps war was the goal of President Polk when he deployed "Old Rough and Ready" Zachary Taylor to the disputed territory. Since The Constitution does not empower the president to launch preemptive wars (Buchanan, 2004, page 19), Polk needed to manufacture his justification. Polk asked Congress for a declaration of war but he was planning to ask for this declaration before word of the "attack" ever reached Washington. Soon after becoming president he ordered the Pacific fleet to stand ready to seize California's ports in the event of war with Mexico (McPhersan, 1988, page 49). 

President Polk's decision to declare war on Mexico sparked vigorous debate among the Congress.There was strong opposition to this policy. Members of both Houses had challenged Polk's thesis "that American blood had been spilled upon American soil." The dissident Congressman doubted that the Mexicans had violated an American boundary or had invaded an American territory. Senator J. Crittenden, Kentucky Whig, had asserted that few members of Congress, when the annexation of Texas was voted, believed that the Rio Grande was the boundary. Representative Garret Davis had flatly insisted the territory between the Nueces and Rio Grande rivers was Mexican. Others held the area was, at best, debatable territory and that in sending Taylor's army into it, President Polk had committed an act of aggression (Dufour, 1968, page 15). In spite of their vocal opposition, both Crittenden and Davis voted "aye" for the war bill and the bill was approved by the Congress. Polk's critics were backed into a corner. They could not afford to appear unpatriotic; many swallowed their outrage and supported war.

Opposition came not only from the Whig party but from Polk's own Democratic Party as well. John C. Calhoun, the South Carolinian and democratic leader, thought the war could have been avoided, and he objected to placing blame upon MexicoWhen the vote was called, Calhoun abstained.

Polk’s political enemies, mainly the Whigs, believed that Polk was responsible for the Mexican War. They believed that Mexico was goaded into war and that it was a predetermined affair. Some Whigs contended that the war was "a deliberately calculated scheme of robbery on the part of the superior power." (Dufour, 1968, page 25). There is some historical justification for this position. In 1844, former speaker of the House James K. Polk pledged to the aged Andrew Jackson that, if nominated by the Democratic Party and elected, he would annex Texas and keep it out of the paws of the British Lion that Jackson feared had designs upon it. Jackson urged the delegates in Baltimore to vote for the "dark horse," Polk, although his own vice president, former president Martin Van Buren, was the front-runner for the nomination (Buchanan, 2006, page 97). Therefore, Polk was bound to this policy before he ever became President.

Announcing that Mexico had fired upon American soldiers on American soil, Polk called on Congress not to declare war but to recognize that a state of war already existed. One of the new Whig congressmen, a lanky, craggy Illinoisian with gray eyes, disheveled black hair, and ill-fitting clothes introduced resolutions calling for information about the exact spot where Mexicans had shed American blood to start the war (McPhersan, 1988, page 48). Abraham Lincoln introduced a resolution in Congress calling on President Polk to inform the House "whether the particular spot of soil on which the blood of our citizens was so shed" belonged to Mexico or the United States. He challenged the president to present evidence that "Mexico herself became the aggressor by invading our soil in hostile array." (Goodwin, 2005, pp. 120 - 121). He later went on to say that, "The President is a bewildered, confounded, and miserably perplexed man. God grant he may be able to show, there is not something about his conscious, more painful than all his mental perplexity!" (Lincoln Speech, page 83).

Ulysses S. Grant stated his bitter oppostion to the annexation of Texas in his memoirs. He considered the war with Mexico to be one of the most unjust ever waged by a stronger against a weker nation.

President Polk believed that the Republic of Texas always claimed the Rio Grande, as her boundary. But even if she had always claimed it, did not Mexico always claim the contrary? So there is a claim against claim and nothing is proven. As Lincoln stated in his address to Congress, "If I should claim your land, by word of mouth, that certainly would not make it mine; and if I were to claim it by a deed which I had made myself, and with which, you had nothing to do, the claim would be quite the same, in utter nothingness." (Lincoln Speech, page 3).

Polk justified his position in the border dispute by claiming that Santa Anna in his treaty with Texas, recognized the Rio Grande, as the western boundary of Texas. The problem with this argument is that Santa Anna was a prisoner of war and could not bind Mexico by a treaty. Mexico never ratified this treaty because they believed it was the product of duress.

Many believed that the war was a conspiracy to extend slavery. However, when the call went out for volunteers to join the military, most came from the western states. If the South was so interested in gaining Texas as a slave state, one would think that they would have sent more troops than they did (Enough Blame, page 2). President Polk was an expansionist who was not concerned with extending slavery. Polk was goal oriented; there were four great measures which he believed would define his administration: one, a reduction of the tariff; another, the independent treasury; a third, the settlement of the Oregon boundary question; and lastly, the acquisition of California (Schlesinger, 1971, pp. 441- 442). By 1846 he had signed a treaty with Great Britain over the Oregon territory, passed the Walker Tariff act, and reestablished an independent Treasury. But before he could reach his goal of acquiring California, a war with Mexico would have to be fought.

Lincoln’s future attorney general, Edward Bates, believed that the true nature of the war was “plunder & conquest.”  When Polk wrote Congress in request for a declaration of war, he said, “We have tried every effort at reconciliation.”(Buchanan, 2006, page 99)  In an attempt at diplomacy, John Slidell was sent to Mexico City in November of 1845 with instructions to gain Mexican recognition of the annexation of Texas with the Rio Grande border.  In exchange the U.S. government would assume the debt owed by Mexico to American citizens.  Polk also offered up to $25 million for California and New Mexico.  However, General Jose Herrera refused to receive Slidell. Polk then ordered Zachary Taylor to move toward the Rio Grande.  Polk knew that with anti-Americanism and nationalism rampant that the Mexican government would refuse to negotiate.  He was merely going through the motions.  He also knew that the Nueces was the true boundary; otherwise he would not have sent John Slidell to negotiate.  Further evidence that the War with Mexico was predetermined can be found in Polk’s own Secretary of State, James Buchanan. Buchanan advised Polk to wait for an overt act by the Mexican hotheads who had overthrown Herrera (Buchanan, 2006, page 99).

In summary, the research above presents strong evidence that  the War with Mexico was a war of conquest in pursuit of the annexation of Texas.  There were several reasons presented for this position: 1) Before becoming the president, James Polk had pledged to Andrew Jackson that he would annex Texas, 2) President Polk had an explicit goal of acquiring Mexican territory in his quest of Manifest Destiny, 3) Polk was planning to ask for a declaration of war before America was attacked by Mexico, 4) Polk’s followers were jubilant when American blood was shed.

Accepting   President Polk’s position for declaring war, would be allowing the President to invade a nation whenever he believes it is necessary.  Although there were many dissenters of President Polk’s decision to declare War with Mexico, perhaps the strongest came from Abraham Lincoln.  His dissent was branded a “treasonable assault upon President Polk.”  It was predicted that Lincoln would have a short political career.

References

Buchanan, P. J. (2004). Where the Right went Wrong.  New York:  St. Martin’s Griffin.

Buchanan, P. J. (2006). State of Emergency.  New York:  St. Martin’s Griffin.

Dufour, C. L. (1968). The Mexican War A Compact History 1846-1848.  New York:  Hawthorn books.

Enough Blame to Go Around: Causes of the Mexican American War. Retrieved October 26, 2006 from www.azteca.net/aztec/war/Mexican-American-War.html.

Goodwin, D. K. (2005). Team of Rivals.  New York:  Simon & Schuster.

Lincoln Speech: The War with Mexico.  Retrieved November 5, 2006 from www.animatedatlas.com/mexwar/lincoln2.html.

McPherson, J.M. (1988).  Battle Cry of Freedom. New York: Oxford University Press

Schlesinger Jr., A. M. (1971). The Age of Jackson.  New York:  Little, Brown and Company.