The most important factor that motivated polk to acquire california as american territory was

Polk was very insistent to acquire California, it is because he very much wanted to start a negotiation between the United States and Mexico. He was even willing to give a threat of war just to be able to push the negotiation.

Polk had proclaimed in 1845 near the start of his presidency that the attainment of California was one of "four great measures" he wanted to achieve while in office. Historian Sam W. Haynes has recognized Polk as a "fitting representative" of the "expansionist impulse" known as the Manifest Destiny. As a situation of the Treaty of Guadalupe Hidalgo, which finished the Mexican War, the administration of Mexico conceded to the U. S. a massive amount of land that contained within the current state of California.