In early 1846, Pres. James K. Polk dispatched an expeditionary force to the border hoping to provoke hostilities. It worked. In April, Mexico declared war. The American Army won two back-to-back victories. The U.S. formally declared war in May, and – after a series of very bloody battles – Mexico was defeated in 1848. America's victory resulted in the vast acquisition of new U.S. territories stretching to the Pacific: A bone of contention for some Mexicans (and other Hispanics) in the current immigration reform debate.