Question

as a result of mexicos refusal to negotiate with slidell, polk ordered general zachary taylor to the rio grande border and a skirmish occurred between the two countries. according to u.s. accounts, the fighting erupted when a mexican cavalry regiment crossed the rio grande and attacked a smaller american cavalry unit. the u.s. forces defeated a mexican army there. in response to this mexican aggression, polk asked congress to declare war against mexico.
what led president polk to take military action at the rio grande border?

Explanation:

Mexico refused to negotiate with U.S. envoy Slidell. This led Polk to order military forces to the Rio Grande border, where a skirmish with Mexican troops occurred, prompting further military action and a war declaration.

Answer:

Mexico's refusal to negotiate with U.S. representative Slidell led President Polk to deploy General Zachary Taylor and U.S. military forces to the Rio Grande border.