Britannica Sources used in this answer

Why did Polk say that Mexico had shed American blood on American soil?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

How the Mexican-American War changed the U.S. forever — Mexican-American War Learn how the Mexican-American War ultimately pushed the United States closer to civil war.

President James K. Polk’s claim that Mexico had "shed American blood on American soil" was a strategic justification for war following a border skirmish in the disputed territory between the Nueces River and the Rio Grande.12

After the United States annexed Texas in 1845, a conflict arose regarding the southern border: Mexico claimed the border was the Nueces River, while the U.S. asserted it was the Rio Grande. In January 1846, James K. Polk ordered General Zachary Taylor to occupy this contested land.21

On April 25, 1846, Mexican forces crossed the Rio Grande and attacked Taylor’s troops, resulting in 16 American casualties. Polk, who had already been preparing a war message based on Mexico's refusal to negotiate, used this incident to argue that Mexico had invaded U.S. territory and committed an act of aggression, thereby securing congressional support for the Mexican-American War.1