All of Mexico Movement

The All of Mexico Movement, or All Mexico Movement, was a political movement to expand the United States to incorporate all of Mexico. It was a controversial aspect of Manifest Destiny that was unable to garner enough political support to encourage adoption. The Mexican-American War (1846–1848) brought the United States and Mexico into conflict over various geopolitical issues, including a desire to invade and annex much of Mexico, that resulted in victory for the United States.

After the US Army took Mexico City, there was renewed enthusiasm for incorporating all of Mexico. There was fierce opposition to the idea within the U.S. Congress on various internal political disputes.

Background
Before US President James K. Polk took office in 1845, the US Congress approved the annexation of Texas. Polk wished to gain control of a portion of Texas, which had declared independence from Mexico in 1836, but it was still claimed by Mexico. That paved the way for the outbreak of the Mexican–American War on April 24, 1846.

US success on the battlefield by the summer of 1847 encouraged calls for the annexation of all of Mexico, particularly by eastern Democrats, who argued that bringing Mexico into the Union would be the best way to ensure peace in the region.

Opposition
The proposal to annex all of Mexico was controversial. Idealistic advocates of Manifest Destiny, such as John L. O'Sullivan, had always maintained that the laws of the United States should not be imposed onto people against their will. The annexation of all of Mexico would violate that principle and find controversy by extending US citizenship to millions of Mexicans.

That debate brought to the forefront one of the contradictions of Manifest Destiny. Identitarian ideas inherent in Manifest Destiny suggested that Mexicans, as people of color, would present a threat to white racial integrity and so were not qualified to become US citizens, but the "mission" component of Manifest Destiny suggested that Mexicans would be improved (or "regenerated," as it was then described) by bringing them into American democracy. Identitarianism promoted Manifest Destiny but was also used to oppose Manifest Destiny.

An example of this identity-based and racist position was that of John C. Calhoun, Senator from South Carolina, former vice president and future spokesperson for southern secession, in which, in his own words in a speech to Congress on January 4, 1848, he explained that: ''[We] have never dreamt of incorporating into our Union any but the Caucasian race the free white race. To incorporate Mexico, would be the very first instance of the kind of incorporating an Indian race; for more than half of the Mexicans are Indians, and the other is composed chiefly of mixed tribes. I protest against such a union as that! Ours, sir, is the Government of a white race.''

Supporters of total annexation of "All Mexico" regarded it as an anti-slavery measure. Many Americans were troubled by Mexico's Catholicism, weak republicanism, and threat of an upsurge in nationalism.

Final result
The controversy was eventually ended by the Mexican Cession, which added the territories of Alta California and Nuevo México to the United States, both more sparsely populated than the rest of Mexico. Like the All of Oregon movement, the All of Mexico movement quickly abated.

The historian Frederick Merk, in Manifest Destiny and Mission in American History: A Reinterpretation (1963), argued that the failure of the All of Oregon and All of Mexico movements indicates that expansion was not as popular as historians have traditionally portrayed it to have been. Merk wrote that belief in the beneficent mission of democracy was central to American history, but aggressive "continentalism" was an aberration supported by only a minority of Americans, mostly Democrats, but opposed by Whigs and some Democrats. Thus, Louisiana Democrats opposed the annexation of Mexico, while those in Mississippi supported it.