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The Mexican War
Digital History ID 547

Author:   James K. Polk
Date:1846

Annotation: Fifteen years before the United States plunged into civil war it fought a war against Mexico that added half a million square miles of territory to the United States. It was the first war the nation fought almost entirely outside its borders. The underlying cause of the war was the inexorable movement of pioneers into the Far West. As citizens of the United States marched westward, they moved into land claimed by Mexico and inevitably their interests clashed with Mexican claims.

The immediate reason for the conflict was the annexation of Texas in 1845. Despite its defeat at San Jacinto in 1836, Mexico refused to recognize Texas independence and warned the United States that annexation would be tantamount to a declaration of war. When Congress voted to annex Texas, Mexico cut diplomatic relations, but took no further action.

President James Polk told his commanders to prepare for war. He ordered naval vessels in the Gulf of Mexico to position themselves outside Mexican ports. Secretly he warned the Pacific fleet to prepare to seize ports along the California coast. Anticipating a possible Mexican invasion of Texas, he dispatched forces in Louisiana to Corpus Christi in south Texas.

Peaceful settlement of the two country's differences still seemed possible. In the fall of 1845, the President offered to pay $5 million if the Mexicans agreed to recognize the Rio Grande River as the southwestern boundary of Texas. Earlier, the Spanish government had defined the Texas boundary as the Nueces River, 130 miles to the north. No Americans lived between the Nueces and the Rio Grande, although many Mexicans lived in the region. Polk also offered $5 million for the province of New Mexico--which included Nevada and Utah and parts of four other states--and $25 million for California. Polk was eager to acquire California because he had been led to believe that Britain was on the verge of making the region a protectorate. It was widely believed that Mexico had agreed to cede California to Britain as payment for outstanding debts.

The Mexican government, already incensed over the annexation of Texas, declined to negotiate. The Mexican president refused to receive an envoy from the United States and ordered his leading commander, General Mariano Paredes y Arrillaga, to assemble an army and reconquer Texas. Paredes toppled the government and declared himself president. But he too refused to deal with the envoy from the north.

Having failed to acquire New Mexico and California peacefully, Polk then ordered Brigadier General Zachary Taylor to march 3000 troops from Corpus Christi to "defend the Rio Grande." Late in March 1846, Taylor set up camp directly across from the Mexican city of Matamoros, on a stretch of land claimed by both Mexico and the United States.

On April 25, a Mexican cavalry force crossed the Rio Grande and clashed with a small Anglo squadron, forcing it to surrender after the loss of several lives. Polk used this episode as an excuse to declare war. Hours before he received word of the skirmish, Polk and his cabinet had already decided to press for war. "Mexico," the President told Congress, "has passed the boundary of the United States, has invaded our territory, and shed American blood upon the American soil." Congress responded with a declaration of war. Polk's war message of May 11, 1846, follows.


Document: The strong desire to establish peace with Mexico on liberal and honorable terms,a nd the readiness of this Government to regulate and adjust our boundary and other causes of difference with that power on such fair and equitable principles as would lead to permanent relations of the most friendly nature, 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....

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 has become necessary to meet a threatened invasion of Texas by the Mexican forces, for which extensive military preparations have 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....

The Mexican forces at Matamoros [south of the Rio Grande River] assumed a belligerent attitude, and on the 12th of April [Mexican] General Ampudia, then in command, notified General [Zachary] 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 sixty-thee men and officers were on the same day dispatched from the American camp....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."

The grievous wrongs perpetrated by Mexico upon our citizens throughout a long period of years remain unredressed, and solemn treaties pledging her public faith for this redress have bene disregarded. A government either unable or unwilling to enforce the execution of such treaties fails to perform one of its plainest duties.

Our commerce with Mexico has been almost annihilated. It was formerly highly beneficial to both nations, but our merchants have been deterred from prosecuting it by the system of outrage and extortion which the Mexican authorities have pursued against them, whilst their appeals through their own Government for indemnity have been made in vain. Our forbearance has gone to such an extreme as to be mistaken in its character. Had we acted with vigor in repelling the insults and redressing the injuries inflicted by Mexico at the commencement, we should doubtless have escaped all the difficulties in which we are now involved.

Instead of this, however, we have been exerting our best efforts to propitiate her good will.... But now, after reiterated menaces, Mexico has passed the boundary of the Untied 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, 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....

In further vindication of our rights and defense of our territory, I invoke the prompt action of Congress to recognize the existence of the war, and to place at the disposition of the Executive the means of prosecuting the war with vigor, and thus hastening the restoration of peace.

Source: James D. Richardson, A Compilation of the Messages and Papers of the Presidents (New York, 1897)

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