After the annexation of the former Republic of Texas was approved in 1845, the United States sent General Zachary Taylor to occupy the area below the Nueces to support its claim to all land east of the Rio Grande. In August 1845 he reached Corpus Christi, where he waited while the United States and Mexico tried to reach a boundary agreement, and he sent engineers to map a road parallel to the Gulf, where the U.S. Navy watched the crisis. His army, the largest U.S. Army fielded in the first half of the 19th century and including on its rosters two later U.S. presidents as well as many later statesmen and generals, remained there through a rainy winter. On orders from Washington, it moved toward the Rio Grande in March 1846 through a sparsely settled country rich in game, including wild cattle, antelope, deer, mustang horses, and wild turkeys. Although challenged about 70 miles south of here by a Mexican patrol, Taylor proceeded to occupy the Rio Grande Valley. April attacks and the May battles of Palo Alto and Resaca de la Palma led the United States to declare war. Afterward many troops took this road and joined the fighting, which fixed the Rio Grande as the boundary and gained for the U.S. lands now in Arizona, California, Nevada, and New Mexico.