Consequences of the Mexican American War and Manifest Destiny

From the specific perspective of Manifest Destiny, the Mexican American War was viewed as a massive success for the United States.
The primary achievement of the war was the creation of a grand American empire that expanded to the point of "rubbing shoulders" with both the Atlantic Ocean and the Pacific Ocean.

The secondary major effect of acquiring western land was the ignition of a bitter dispute regarding whether slavery should be permitted in those new territories.
The Wilmot Proviso (1846): - This congressional battle began even before the conclusion of the Mexican American War. - Pennsylvania Congressman David Wilmot introduced a "rider" to a funding bill. - The proviso mandated that slavery be banned in all lands gained during the war with Mexico. - Although the Wilmot Proviso was ultimately voted down, it was perceived as a "proper smack in the face" to Southern representatives. - Southern representatives desired these lands for the expansion of slavery to protect their specific interests and maintain power within the government.

Southern Democrats, described as "slavery loving," had varying reactions to the Treaty of Guadalupe Hidalgo: - Expansionist Extremism: Some members opposed the treaty because it did not go far enough. They argued that because the expansion of slavery was vital for their survival and political power, the United States should have taken the entirety of Mexico to expand the institution of slavery as far south as possible. - Racial and Citizenship Concerns: Others, such as John C. Calhoun, struggled with the racial implications of the Mexican cession.

John C. Calhoun was a staunch "slave power man" who wanted the institution of slavery to spread extensively.
Despite his pro-slavery stance, he held significant worries regarding the Mexicans and American Indians already populating the lands gained in the victory.
Calhoun’s concerns were not based on the safety or well-being of these populations; rather, they were based on racial exclusion.
The "White Man’s Domain": Calhoun believed the United States was exclusively the domain of white men.
He could not accept the prospect of offering United States citizenship to the many Mexicans residing in the newly acquired territories.
Long-term Impact: The conflict over slavery's expansion became so divisive that slave-holding states eventually chose to secede from the Union to form their own country where slavery would remain untouched.

The third major effect of the war was the eruption of conflict with Mexicans and American Indians.
The Myth of Open Land: Despite rhetoric describing Western territories as "open and unpopulated," the lands of the Mexican cession were densely populated.
As soon as the territory transitioned from Mexican to United States control, conflicts began immediately.

The Comanche Threat: The Comanche nation was identified as the most persistent threat to settlers.
Even before the US acquisition, the Comanches were harassing settlers in Texas and Northern Mexico.
Justification for Expansion: Because the Comanches regularly raided Mexican settlements and undermined the local economy in the North, US expansionists argued that seizing the land and "taming" the Comanche was a noble and charitable act for the Mexican residents.
Military Subjugation: Once the US took possession of the territory, American troops engaged in a series of conflicts with the Comanche and Kiowa.
These conflicts lasted until the $1870s$ .
Indigenous groups were ultimately conquered through two primary means: - American military power. - Ravaging diseases contracted from westward-migrating Americans.

During the Texas Revolution, white American settlers known as Anglos fought alongside Mexican natives known as Tejanos.
Tensions grew after independence was achieved and Texas became the "twentieth" state to join the United States.
Citizenship Discrepancies: - The Treaty of Guadalupe Hidalgo stipulated that all former Mexican citizens in the Mexican cession would become US citizens. - However, individual states retained the power to create their own citizenship laws. - States quickly moved to ban everyone except white Mexican men from obtaining citizenship.
Land and Social Marginalization: - Anglos, seeking new soil, expelled many Tejanos from their land. - Tejanos were marginalized within Texas society. - Efforts were made to force Tejanos to assimilate into white American culture. - Some Tejanos submitted by sending children to American schools or attempting to convert to Protestantism. - Most assimilation efforts failed, and Tejanos were largely demoted to the status of unskilled agricultural laborers.

Resistance to Anglo dominion occurred, most notably through Juan Cortina.
Juan Cortina: A wealthy Mexican landowner who held territory on both sides of the Rio Grande.
When Texans began claiming land for themselves on the American side of the border, Cortina launched a series of conflicts known as the Cortina Wars.
These wars were aimed at resisting American expansion and involved US forces and the Texas Rangers.