Following the failure of John Slidell’s mission,…

Following the failure of John Slidell’s mission, President Polk had ordered General Zachary Taylor to occupy the territory between the Nueces River and the Rio Grande, which he had done on March 28, 1845.

Abolitionists claim that Polk’s move is a hostile and aggressive act of provocation designed ultimately to gain a new slave territory for the United States.

A few Federalist leaders had contacted Taylor while he while he was camped along the Nueces River in the spring, promising supplies and asking for American support in overthrowing Mariano Paredes.

On April 4, Paredes had ordered his commander at Matamoros to attack Taylor; the commander delayed, Paredes had replaced him, issued a declaration of war on April 23, and reordered the attack.

The Mexicans had crossed the Rio Grande and ambushed a platoon of dragoons on April 25, 1846.

The Americans had quickly repulsed two more attacks at Palo Alto and Resaca de la Palma on May 8—9, defeats that had surprised and dismayed the Mexican leaders.

Paredes blames his commanding general for the defeat by the outnumbered U.S. force rather than acknowledge the effectiveness of American light artillery.

The Matamoros garrison, with a new commanding general, evacuates to the south.