3 - call for a treaty with Mexico
Explanation:
President James Polk called for a treaty with the Mexican government which was called as Treaty of Guadalupe. This treaty ended the Mexican-American war that took place during 1846-48.
Gaining the territories of California and New Mexico from Mexico was one of the major goals of President James.
Mexico signed a treaty with America in which it recognized Rio Grande southern border of America. In the same treaty, Mexico ended up with giving California, New Mexico, Arizona, Colorado, Utah, Nevada and Wyoming to America in exchange of $15 million.
