The  War with Mexico

For the next ten years, the Mexicans and Americans could not agree on a border where Texas ended and  Mexico  began.  In 1845, Texas joined  the United States.  

A year late, the border fight between  Texas and Mexico grew into and war  between Mexico and United States.  The war lasted two years .  Battles took place all the way from Mexico city to Northern California.  The Mexicans lost the war and they were forced  to give up all their land north of the Rio Grande. This included  California and New Mexico.

Some American leaders were greedy and wanted to continue the war and take  over  of the Mexico.  Others felt that the United States had already taken to much. They said that the war had started over Texas and that it was unfair to take  California   as well.  But they never gave Mexico their land back. 

The states and territories of America stretched from the Atlantic  to the Pacific, and from Canada to Mexico.