What reason did President James K. Polk give when he asked Congress to declare war against Mexico?

Declarations of war, May 1846

His message to Congress on May 11, 1846, claimed that "Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon American soil."

Explanation:

Polk used a sneaky, yet clever plan to get the Americans to go to war with Mexico. He wanted Mexico to strike first and declare the war because the two countries argued over the Texas and Mexico border. The United States thought it was the Rio Grande that separated the two countries, while Mexico thought differently.