upon Manifest Destiny. Manifest Destiny is the belief that America had a God-given destiny to expand
the country's borders from sea to shining sea. The war had two major causes.
The first major cause was the desire to expand the United States would cause conflict with the
British in Canada, to the Mexicans in the southwest, and the Native Americans. Ever since President
Jefferson acquired the Louisiana Territory in 1803, more and more Americans migrated westward.
President Polk became President in 1845, the idea of expanding the United States' borders came into
favor among him and the American people. In both 1835 and 1845, the United States offered to
purchase California from Mexico for five million dollars and twenty-five million dollars. The Mexican
government turned down the United States' offer.
Tension grew between Mexico and the United States when Texas became a United States' state.
The second major cause of the war was the Texan War of Independence and the area to the United
States. Not all American migration was unwelcome. In the 1820's and 1830's, Mexico needed people in
the Northern parts of the country. An invitation was issued for people who would take an oath of
allegiance to Mexico and convert to Catholicism. Thousands of Americans liked this offer and moved,
often with slaves, to the Mexican Province of Texas. Many of the people soon became mad with the
way the government in Mexico city tried to run the province. In 1835, Texans fought and after many
bloody battles, the Mexican President Santa Anna signed the Treaty of Velasco in 1836. Texas gained
its independence but Mexicans refused to accept the document. This triggered many border fights
against Texas and Mexico. The Americans became unhappy with the Mexicans because of the conflicts.
Texas joined the United States...