USA HISTORY

Detailed explanation-1: -It stemmed from the annexation of the Republic of Texas by the U.S. in 1845 and from a dispute over whether Texas ended at the Nueces River (the Mexican claim) or the Rio Grande (the U.S. claim).

Detailed explanation-2: -Texas claimed the Rio Grande as its southern border. Mexico said the Nueces River, to the north, should be the border. The dispute simmered until Dec. 29, 1845, when the U.S. annexed the Lone Star State, and sent troops to the Rio Grande a month later.

Detailed explanation-3: -Mexico refused to recognize the Republic of Texas, and intermittent conflicts between the two countries continued into the 1840s. The annexation of Texas as the 28th state of the United States, in 1845, led directly to the Mexican–American War.

Detailed explanation-4: -In 1845 the United States annexed Texas and subsequently engaged in a dispute with Mexico over the southern Texas-Mexico border. Texas claimed that its southwest boundary extended to the Rio Grande. Mexico claimed that the boundary was the Nueces River, which is 100 miles (160 kilometers) eastward.

Detailed explanation-5: -The U.S. sent troops to the disputed Rio Grande, ignoring Mexican demands to withdraw. Mexico subsequently attacked a group of 80 soldiers on April 25, 1846, a move which Polk used to convince the Congress of the United States to declare war.