Question

What was a main issue that started the Mexican War?

the Mexican army invaded Texas
the U.S. attacked and captured Mexico City
the dispute over the border between the U. S. and Mexico

Answer 1

the dispute over the border between the U. S. and Mexico

The U.S. claimed the Rio Grande as its border, while Mexico. claimed Nueces River as it's border, and on April 25, 1846 both armies met at the Rio Grande and the Mexican American War began.

Answer 2

Dispute over the border between the two