The Mexican American War was officially terminated on February 2, 1848, by Guadalupe Hidalgo's contract, in favor of the United States. Although the war was successful for America, President Polk lost public support because of two years of bloody and expensive war. He was succeeded by Zachary Taylor, the hero of the Mexican American War. In addition, this war has again triggered a debate about slavery, which resulted in a civil war.
The answer is: D. slavery in the United States
