The Mexican-American War lasted only 15 months, but the spoils -- good and bad -- have proved to be long lived. Mexico lost the largest gold mine in the continental U.S., along with a huge mass of territory, the acquisition of which proved to be a significant point of contention that provoked both sides of the American Civil War.

New Lands Under Manifest Destiny

After The United States took Mexico City in September of 1847, President James K. Polk ordered Chief Clerk of The Department of State Nicholas P. Trist back to Washington, D.C. Trist, however, remained in Mexico against orders and continued to negotiate a peace treaty. Trist was eventually able to cement a treaty -- known as the 1848 Treaty of Guadalupe Hidalgo -- that declared Mexico's official surrender, and sold the regions of New Mexico and Upper California to the United States for 15 million dollars. These territories became the American states of New Mexico, California, Arizona, and sections of Wyoming, Colorado, Utah and Nevada.

The Slavery Debate

The Mexican-American War reinvigorated arguments between the Northern and Southern states regarding slavery. In 1846, Pennsylvania Congressman David Wilmot presented his Wilmot Proviso, which sought to forbid any lands acquired in the war from condoning slavery. Congress never passed The Wilmot Proviso, but its introduction -- according to American historian Dr. Drew VandeCreek -- sparked ideas in Southerners of a Northern conspiracy against the South, and significantly helped to divide the nation on the subject of slavery, which ultimately led to the American Civil War.

Monumental Loss

Mexico lost every battle during the Mexican-American War, and after the United States captured Mexico City, the U.S. flag flew over the Mexican National Palace. Mexico's losses, however, didn't end with lost battles, injured pride or territories of land. Mexicans, as well as Tejanos -- Mexicans who lived in Texas -- became victims of full-scale racial prejudice. To make matters worse, shortly after the war ended, gold was discovered in California, which inspired the famous California Gold Rush. This monumental sum of wealth that would have belonged to Mexico now belonged to the United States.

Not-So-Long Established Borders

In addition to securing new states for the country, the Treaty of Guadalupe Hidalgo fixed what ended up being the geographical framework for the lower 48 states, or at least it tried. The Texan-Mexican stretch of this border was the Rio Grande River, which became a long-term point of contention known as the Chimazel Dispute. In 1852, the river was surveyed by cooperating Mexican and U.S. surveyors, but by 1864 the river's channel had shifted, and called the border into question: Was the original survey to be followed, or the current channel of the river? After several failed arbitration attempts, a compromise was finally reached in 1963, in which the disputed land was divided and awarded to each country.