What action did President Polk take that resulted in the war between the United States and Mexico?

He ordered troops to invade Mexico and capture Vera Cruz and Mexico City.

He refused to return Mexican land that had been turned over by Santa Anna.

He tricked General Santa Anna into bringing troops across the U. S. border.

He sent General Zachary Taylor to claim an area of disputed land for the United States.

Is it A?

He sent General Zachary Taylor to claim an area of disputed land for the United States and this step of President Polk resulted in the war between the United States and Mexico. The correct option among all the options given in the question is the last or the fourth option. The main target behind making California a part of the United States was the San Francisco Bay. Mexico did not like the way United States was trying to acquire California as the Mexicans thought it to be a part of their country.