The U.S. belief that Mexico was encouraging raids by Native American tribes on U.S. settlements had a significant effect on the Mexican-American War. This belief led to a heightened sense of tension between the two countries, and ultimately led to the U.S. declaring war on Mexico in 1846. The U.S. saw the raids as a direct threat to its sovereignty and security, and used this as justification for the war. The war resulted in the U.S. gaining a large amount of territory from Mexico, including California, Arizona, New Mexico, and parts of Colorado, Nevada, and Utah.
