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Debating the Mexican-American War, May 1846

Use this primary source text to explore key historical events.

Suggested Sequencing


On May 11, 1846, President James K. Polk sent a special message to Congress asking for a declaration of war against Mexico. In his message, the president outlined a series of grievances against the Mexican government and argued that the Mexicans had started a war by attacking U.S. soldiers in southern Texas. Congress declared war two days after the message, but the debate continued over the war and the expansion of slavery in the West. Congressman Joshua Giddings of Ohio issued a scathing reply to Polk two days later and accused the president of starting a war of conquest to safeguard slavery. Giddings was not alone in his beliefs; many northerners and opponents of slavery especially feared that the conflict was an excuse for the expansion of slavery.

Sourcing Questions

  1. Who was the speaker in these two documents?
  2. What was the goal of each speaker in their respective speeches?

President Polk, War Message to Congress, May 11, 1846

Vocabulary Text
envoy (n): a diplomatic representative The strong desire to establish peace with Mexico on liberal and honorable terms . . . induced me in September last to seek the reopening of diplomatic relations between the two countries. . . . An envoy of the United States repaired to Mexico with full powers to adjust every existing difference. But though present on the Mexican soil by agreement between the two Governments, invested with full powers, and bearing evidence of the most friendly dispositions, his mission has been unavailing. The Mexican Government not only refused to receive him or listen to his propositions, but after a long-continued series of menaces have at last invaded our territory and shed the blood of our fellow-citizens on our own soil. . . .
Nueces and the Del Norte: The Nueces River is the southernmost river north of the Rio Grande. The Del Norte river refers to the Rio Grande, or Río Grande del Norte, as it is known in Mexico. In my message at the commencement of the present session I informed you that upon the earnest appeal both of the Congress and convention of Texas I had ordered an efficient military force to take a position “between the Nueces and the Del Norte.” This had become necessary to meet a threatened invasion of Texas by the Mexican forces, for which extensive military preparations had been made. The invasion was threatened solely because Texas had determined, in accordance with a solemn resolution of the Congress of the United States, to annex herself to our Union, and under these circumstances it was plainly our duty to extend our protection over her citizens and soil.
This force was concentrated at Corpus Christi, and remained there until after I had received such information from Mexico as rendered it probable, if not certain, that the Mexican Government would refuse to receive our envoy.
Rio del Norte: The Rio Grande River, which forms the present-day boundary between Texas and Mexico Meantime Texas, by the final action of our Congress, had become an integral part of our Union. The Congress of Texas, by its act of December 19, 1836, had declared the Rio del Norte to be the boundary of that Republic. Its jurisdiction had been extended and exercised beyond the Nueces. The country between that river and the Del Norte had been represented in the Congress and in the convention of Texas, had thus taken part in the act of annexation itself, and is now included within one of our Congressional districts. Our own Congress had, moreover, with great unanimity, by the act approved December 31, 1845, recognized the country beyond the Nueces as a part of our territory by including it within our own revenue system, and a revenue officer to reside within that district has been appointed by and with the advice and consent of the Senate. It became, therefore, of urgent necessity to provide for the defense of that portion of our country.
Accordingly, on the 13th of January last instructions were issued to the general in command of these troops to occupy the left bank of the Del Norte. This river, which is the southwestern boundary of the State of Texas, is an exposed frontier. From this quarter invasion was threatened; . . .
The Army moved from Corpus Christi on the 11th of March, and on the 28th of that month arrived on the left bank of the Del Norte opposite to Matamoras, where it encamped on a commanding position . . .
dragoon (n): a mounted soldier who also fought on foot (as opposed to cavalry who fought mainly on horseback) The Mexican forces at Matamoras assumed a belligerent attitude, and on the 12th of April General Ampudia, then in command, notified General Taylor to break up his camp within twenty-four hours and to retire beyond the Nueces River, and in the event of his failure to comply with these demands announced that arms, and arms alone, must decide the question. But no open act of hostility was committed until the 24th of April. On that day General Arista, who had succeeded to the command of the Mexican forces, communicated to General Taylor that “he considered hostilities commenced and should prosecute them.” A party of dragoons of 63 men and officers were on the same day dispatched from the American camp up the Rio del Norte, on its left bank, to ascertain whether the Mexican troops had crossed or were preparing to cross the river, “became engaged with a large body of these troops, and after a short affair, in which some 16 were killed and wounded, appear to have been surrounded and compelled to surrender.” . . .
We have tried every effort at reconciliation . . . But now, 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.
As 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.

Congressman Joshua Giddings, Debate on the Mexican War, House of Representatives, Washington, May 13, 1846

I apprehend that much blood and much treasure will be expended before the people of New Mexico will be compelled to unite with slave-holding Texas. Those Mexicans love freedom. They have abolished slavery, for which they entertain an unconquerable detestation. . . .
But the President says this Mexican country “is now included in one of our congressional districts.” These thirty thousand people who, so soon as the bill which passed this House yesterday shall receive the sanction of the Senate, and shall be approved by the President, will be in a state of war with this nation, are to be represented on this floor because Texas has on paper attached them to one of her congressional districts. . . .
I regard the message as having been put forth to divert public attention from the outrage committed by the President upon our own Constitution, and the exercise of usurped powers, of which he has been guilty in ordering our army to invade a country with which we are at peace, and of provoking and bringing on this war. I am led to this inevitable conclusion from the fact that he dare not rest his justification upon truth. He reminds us of the grievous wrongs perpetrated (as he says) by Mexico upon our people in former years . . . all for the purpose of justifying himself in sending the army to the Rio Grande, and commencing the work of human butchery! . . .
Sir, no man regards this war as justWe know, the country knows, and the civilized world are conscious, that it has resulted from a desire to extend and sustain an institution on which the curse of the Almighty most visibly rests. Mexico has long since abolished slavery. She has purified herself from its crimes and its guilt. That institution is now circumscribed on the southwest by Mexico, where the slaves of Texas find an asylum. . . . It has therefore become necessary to extend our dominions into Mexico in order to render slavery secure in Texas. . . .
This war is waged against an unoffending people, without just or adequate cause, for the purposes of conquest; with the design to extend slavery; in violation of the Constitution, against the dictates of justice, of humanity, the sentiments of the age in which we live, and the precepts of the religion we profess. I will lend it no aid, no support whatever. I will not bathe my hands in the blood of the people of Mexico, nor will I participate in the guilt of those murders which have been and which will hereafter be committed by our army there. For these reasons I shall vote against the bill under consideration and all others calculated to support this war.

Comprehension Questions

  1. Why was it necessary to station U.S. troops between the Nueces and the Del Norte Rivers?
  2. According to Polk, when did the U.S. troops move from their position?
  3. Where had the Congress of Texas set its boundary?
  4. What two reasons does Polk give to justify this boundary from the perspective of Texas?
  5. What additional reasons does Polk give to justify this boundary?
  6. What was the immediate cause of this conflict, according to General Ampudia’s warning to General Taylor?
  7. Do you think it is clear from this account who fired first?
  8. According to this passage, how did Mexico start this conflict?
  9. What reasons does Polk give for Congress to declare war?
  10. What does Giddings accuse President Polk of doing?
  11. What does Giddings think the purpose of this conflict was?

Historical Reasoning Questions

  1. Compare the tone of the two speeches. How does each serve to further the author’s message?
  2. After the Mexican-American War began, Pennsylvania congressmen David Wilmot introduced the following rider to a funding bill for the war in 1846. Though it passed the House of Representatives, it did not pass the Senate:

    Provided that, as an express and fundamental condition to the acquisition of any territory from the Republic of Mexico, by the United States, by virtue of any treaty which may be negotiated between them, and to the use by the Executive of the moneys therein appropriated, neither slavery nor involuntary servitude shall ever exist in any part of said territory, except for crime, whereof the party shall first be duly convicted. —Wilmot Proviso, 1846

    What does this bill assume about the outcome of the war?

  3. Did Wilmot agree with Polk’s or Giddings’s explanation for the war? Explain.
  4. Unlike Giddings, Polk never mentions slavery in his address. Why do you think the president focused on the issue of national sovereignty and security in his speech?

Polk’s War Message:


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