Why the Mexican-American War Was Controversial

The 1846–1848 war sparked deep division in the U.S. over:

• Manifest Destiny: Critics called it imperialist land-grabbing; supporters saw it as divine expansion.
• Slavery: Northerners (Whigs, abolitionists) feared new slave states; Southerners wanted territory for slavery's expansion. The Wilmot Proviso (banning slavery in new lands) failed but intensified sectionalism.
• Mexican Rights: Mexican citizens in annexed territories lost land, faced discrimination, and were denied citizenship promises.
• Conduct: U.S. troops committed atrocities (e.g., massacres, looting), condemned by contemporaries like Ulysses Grant and Abraham Lincoln.

The war added 525,000 sq mi but poisoned U.S.-Mexico relations and accelerated the path to Civil War.