Spanish settlement of the west International borders has always been centers of conflict, and the U.S.-Mexican border is no exception. With the European colonizing the New World, it was a matter of time before the powers collided. The Spanish settled what is today Mexico, while the English settled what is today the United States. When the two colonial powers did meet became what is today the United States' Southwest, it was not England and Spain. Rather the two powers were the United States and Mexico. Both Counties had broken off from their mother countries. The conflict that erupted between the two countries where a direct result of different nation policies.
The United States had a policy of westward expansion, while Mexico had a policy of self-protection. The Americans never had a written policy of expansion. What they had was the idea of "Manifest Destiny." Manifest Destiny was the belief that the United States had the right to expand westward to the Pacific Ocean.
On the other hand, Mexico was a new country wanting to protect itself from outside powers. Evidence of U.S. expansion is seen with the independence of Texas from Mexico. The strongest evidence of U.S. expansion goals is with the Mexican-American War. From the beginning, the war was conceived as an opportunity for land expansion. Mexico feared the United States expansion goals (Gibson 25-88).
During the 16th century, the Spanish began to settle the region. The Spanish had all ready conquered and settled Central Mexico. Now they wanted to expand their land holdings north. The first expedition into the region, that is today the United States Southwest, was with Coronado. Coronado reported a region rich in resources, soon after people started to settle the region. The driving force behind the settlement was silver in the region.