The Mexican War fulfilled the American desire to create a continental empire. The war united the country in a way similar to 911 or Pearl Harbor. Despite this, the nation began ripping itself apart following the conflict with Mexico. America won a dramatic victory. However, that victory led to the fracturing of the country and provided battlefield experience for several Civil War generals. It also provided a resume builder for several presidential candidates over the next decade. Over the next dozen years, the main political issue transitioned from Manifest Destiny to slavery. In the end, the Mexican War led to American expansion to the Pacific Ocean and then fractured the nation over slavery.
The United States and Mexico negotiated the Treaty of Guadalupe Hidalgo to end the war. The U.S. army occupied Mexico City leaving the Mexican government in a lurch. America would get whatever it wanted. In the subsequent Mexican Cession, the United States gained over a half million square miles of territory representing over 50% of Mexico. Eventually, this land made up part of Colorado, Arizona, New Mexico, and Wyoming and included all of California, Nevada, and Utah. In return, Mexico received $15 million. Mexican citizens that remained in the cession were guaranteed their property rights, but this was later ignored. In 1853, the United States made the Gadsden Purchase which included parts of New Mexico and Arizona completing the American southwest.
In the United States, some wanted to annex all of Mexico. Others wanted to take Northern Mexico. This was too much for many and the movement failed. Additionally, some northerners worried slavery would expand into the new territory. In the early months of the conflict, Congressman David Wilmont of New York introduced a proviso which would have banned slavery in any territory acquired in the war. The proviso was a rider on the war spending bill. The North dominated the House of Representatives and passed the Wilmont Proviso. However, the South blocked it in the Senate. Some northerners attempted to include it in the Treaty of Guadalupe Hidalgo, but that failed as well. As a result, slavery would become the dominant political issue for the next dozen years leading up to the Civil War.
The Mexican War also set up the Civil War by providing a training ground for officers. Many future military commanders of the Civil War served in Mexico. Anti-war Ulysses S. Grant defeated the Confederacy in 1865. Other northern generals that served in the Mexican War included George B. McClellan, Ambrose Burnside, and George Gordon Meade. Southern generals included Robert E. Lee, Thomas “Stonewall” Jackson, and James Longstreet. Mexican veteran Jefferson Davis became the Confederate president.
While Davis assumed the Confederate presidency, the war produced three presidents and three failed presidential candidates. The war’s greatest hero, Zachary Taylor, won the presidency in 1848. General Franklin Pierce defeated General Winfield Scott in 1852. Ulysses S. Grant won two terms as president, but that was based on his Civil War service. John C. Fremont was the first Republican candidate for president losing to James Buchanan. 1860 candidate John C. Breckinridge served in the Kentucky volunteers.
The Mexican War was a wildly popular conflict. The United States won a dramatic victory and produced many heroes. Some of those heroes ran for president. Others returned to normal life. Following the war, North and South began conflicting over slavery and the expansion of the institution. The victory in the war opened Pandora’s Box and America eventually reaped the whirlwind. Slavery ripped America apart and many of those Mexican War vets would fight against one another in the Civil War.