The United States and Mexico could not agree on the border
between them.The United States claimed that Mexican
soldiers crossed over to attack some American soldiers. Some
in the United States said it was just an excuse to get land
claimed by Mexico. Others feared that the practice of slavery
would spread to new land gained by war.
Most of Congress as well as President Polk were for the
war.They believed in Manifest Destiny, and Polk wanted
California. In May 1846, the United States declared war.
It became known as the Mexican–American War.
News of the war took more than a month to reach
California. On July 2, Commodore John D. Sloat, a
commander of U.S. Navy ships in the Pacific, waited for
news. He had orders to take California ports when war
broke out. He decided to take action on July 7, and raised
the American flag over Monterey.Yerba Buena and San
Francisco Bay were captured, and Commodore Robert
Stockton took San Diego and Los Angeles. Thus the
Success of the Americans Caused for the Mexicans to
eventually surrender and sign a treaty.