What were the causes and consequences of the Mexican War?

The Mexican-American War was a "question of righteousness". On May 9th, 1846 President James K. Polk delivered a war message to Congress, stating that "Mexico has passed the boundary of the United States, has invaded our territory, and shed American blood upon the American soil." President Polk sent John Slidel to Mexico to negotiate a settlement. Slidell was authorized to purchase California and New Mexico, part of which was claimed by Texas, and to offer the …

…led to stress of popular sovereignty and the Civil War. When the U.S. decided to move westward, they should have foreseen all that was going to happen. The war with Mexico, and the Civil war should have been expected. Though Manifest Destiny did expand the U.S. from the Atlantic to the Pacific, it also stressed popular sovereignty in the undecided states of texas, california, and Oregon, which later led to the Civil War.