CAUSES OF THE MEXICAN WAR
There was more than just one event that caused the Mexican-American War. The greatest reason that Mexico declared war on the U.S. was the annexation of Texas to the United States. Another reason that Mexico declared war was because neither country could decide what the boundary between Texas and Mexico should be (Nueces River or Rio Grande?) Lastly, there had been damage done to American property located in Mexico, and as a result of all of these occurrences, a war with Mexico was unavoidable. Officially, Mexico declared war on the United States on April 23, 1836; the U.S. declared war exactly 20 days after.