In the US-Mexican War, which two rivers were claimed as borders by each side?

• A. Nueces River and Rio Grande
• B. Mississippi River and Missouri River
• C. Colorado River and Rio Grande
• D. Gulf of Mexico boundary

Answer: (A)

Disputes over where a national border runs can pull countries into war. In the US–Mexican War, the two sides disagreed about which river should mark the Texas–Mexico boundary. The United States (and Texas) claimed the border followed the Rio Grande, meaning lands south of that river were part of Texas. Mexico argued the border lay along the Nueces River, which is farther north, so the land between the Nueces and the Rio Grande was Mexican territory. This clash over which river defined the boundary helped spark the fighting. The two rivers involved are the Nueces River and the Rio Grande.