5.3: Mexican-American War

5.3: Explain the causes and effects of the Mexican– American War.

In the last set of notes, we talked about Manifest Destiny, Texas, and Oregon, and now we’re going to be moving on to the consequences of Texas: the Mexican-American War.

Mexican-American War

So what caused the Mexican-American War? Well, after Texas declared its independence from Mexico, Mexico didn’t want to concede total defeat and so while they were fine with Texas being independent, they didn’t want it annexed by the United States. So that’s why, for almost a decade, Texas remained independent on its own. Presidents Jackson, Van Buren, Harrison, and Tyler all were against annexation, and it took until the election of Polk in 1844 that Tyler started pushing for Texas’s annexation. So when Polk took office, Mexico wasn’t happy about the annexation and so Polk sent John Slidell, a diplomat, to Mexico City to try and get Mexico to sell more territory (New Mexico and California) to the United States, which Mexico refused, and to also establish what the border between Texas and Mexico would be. Mexico said that the border ran along the Nueces River, while the United States said it ran along the Rio Grande, and so as a result, when Polk sent General Zachary Taylor to station troops at the Rio Grande, there was a border conflict and in the end, eleven Americans were dead. In the end, it was this border dispute that led to Congress granting the Mexican-American War in 1846. And like most of the wars leading up to now, what happened during it isn’t really all that important to know so we won’t go over that. Under the leadership of General Winfield Scott, America occupied Mexico City and this led to the signing of the Treaty of Guadalupe Hidalgo in 1848, which did two key things.

  • It established the Rio Grande as the southern border of Texas

  • It outlined the Mexican Cession, in which the California and New Mexico Territories were ceded to the U.S. for 15 million dollars.

Wilmot Proviso

During the Mexican-American War, some Americans predicted that the U.S. would be victorious and gain a significant amount of new territory. As a result, in 1846, Congressman David Wilmot proposed the Wilmot Proviso, which aimed to prohibit slavery in any land acquired from the war. Although it was ultimately rejected, many Southerners interpreted the Proviso as another attempt by Northerners to attack slavery. Although not all Northerners were abolitionists, many supported the concept of free soil, which meant providing land for settlers to live on without competition from slavery. This Proviso was one of the early events that contributed to the build-up to the Civil War.

Later in 1853, the Gadsden purchase would be made where the southern portions of modern-day Arizona and New Mexico would also be sold to the U.S. and in the end, Mexico lost more than half of its territory in total to the U.S.

Although the Treaty of Guadalupe Hidalgo had established that all Mexicans living in the territory would be granted U.S. citizenship, the Native Americans living there wouldn’t be granted citizenship until the 1930s. Even with citizenship, many Mexicans in the territory lost land to white settlers and faced discrimination.