Mexican American War
After being elected in 1844, James Polk wanted to start expanding our country, originally starting with Oregon, and then moving on to California and New Mexico. At first, Polk peaceably offered to buy the land from Mexico because hardly anyone lived there and Mexico did not have much use for it. But, Mexico refused, which was one of the many reasons leading up to the Mexican-American War. The three main causes of the war were there was a dispute between Mexico and the US on the border of Texas, the annexation of Texas, and Polk's desire for the land of California and New Mexico.
The unofficial start of the war occurred in April 1846, when Mexican soldiers fired on US troops. This led US General Kearny to invade New Mexico, where his troops defeated the Mexicans and gained control of New Mexico. In California a rebellion against the Mexican rule took place, led by John Fremont. Fremont joined forces with Kearny, and together they took control of California too. General Zachary Taylor, who later became president of the US, took 6,000 American troops into Mexico and met the Mexican army of 20,000 in Santa Anna. The United Sates ended up controlling northern Mexico after a battle near Buena Vista. Another general, General Winfield Scott, headed for Mexico City, the capital. After meeting resistance at the Fort of Chapultepec in September 1847, Americans also captured Mexico City.
The unofficial start of the war occurred in April 1846, when Mexican soldiers fired on US troops. This led US General Kearny to invade New Mexico, where his troops defeated the Mexicans and gained control of New Mexico. In California a rebellion against the Mexican rule took place, led by John Fremont. Fremont joined forces with Kearny, and together they took control of California too. General Zachary Taylor, who later became president of the US, took 6,000 American troops into Mexico and met the Mexican army of 20,000 in Santa Anna. The United Sates ended up controlling northern Mexico after a battle near Buena Vista. Another general, General Winfield Scott, headed for Mexico City, the capital. After meeting resistance at the Fort of Chapultepec in September 1847, Americans also captured Mexico City.
Treaty of Guadalupe Hidalgo
The Treaty of Guadalupe Hidalgo was signed in 1848, which ended the war, and required Mexico to give up the Mexican Cession which included present-day Texas, California, Nevada, Utah, Arizona, and New Mexico, as well as parts of Colorado and Wyoming. The US only paid Mexico $15 million for the land, and Mexico only kept what is present-day Mexico.
The Gadsden Purchase
In 1853, an American politician named James Gadsden purchased the strip of land under Arizona for $10 million, creating the present-day southwest border between the US and Mexico. This land was valuable because it was relatively flat, which helped railroad builders finish the transcontinental railroad.