The Mexican government had long warned that annexation would mean war with the United States. When Texas joined the U.S., the Mexican government broke diplomatic relations with the United States. The United States now assumed the claims of Texas when it claimed all land north of the Rio Grande. In June 1845, President James K. Polk sent General Zachary Taylor to Texas, and by October, 3,500 Americans were on the Nueces River, prepared to defend Texas from a Mexican invasion. On November 10, 1845, Polk ordered General Taylor and his forces south to the Rio Grande, into disputed territory that Mexicans claimed as their own. Mexico claimed the Nueces River—about north of the Rio Grande—as its border with Texas.