USA HISTORY

Detailed explanation-1: -The border was established in the 1819 Adams–Onís Treaty between the United States and Spain, which specified a border in the vicinity of the western edge of the Mississippi River watershed. Mexico gained its independence from Spain, and the border was reaffirmed in the 1828 Treaty of Limits.

Detailed explanation-2: -Mexico relinquished its claims on Texas and accepted the Rio Grande as its northern border with the United States.

Detailed explanation-3: -Lasting from 1846-1848, the Mexican-American War ended in the Mexico-U.S. border being set at the Rio Grande and the signing of the Treaty of Guadalupe Hidalgo. As part of the Treaty, Mexico lost a devastating 55% of its land to the U.S., giving both countries the border we recognize today.

Detailed explanation-4: -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.