Grade-school history review: In 1846, the U.S. provoked a war with Mexico under President James Polk who wanted to expand U.S. territory all the way to the Pacific. By 1848, the U.S. had captured Mexico City, capital of Mexico, and the U.S. won the war. Mexico then ceded all of the land between Texas and California to the U.S.. The Mexican cession to the U.S. was about 750,000 sq. miles, as compared with the Louisiana Purchase which was about 825,000 sq. miles. The war ended on February 2nd, 1848. Bad luck for Mexico, as gold was discovered in California the week before on January 24th.