How did President Polk promot/increase expansion of the U.S.?

Answer 1

Polk was committed to expansion—Democrats believed that opening up more farms for yeoman farmers was critical for the success of republican virtue. (See Manifest Destiny.) To balance the interests of North and South he sought the Oregon territory (comprised of present-day Oregon, Washington, Idaho, and British Columbia), as well as Texas. He sought to purchase California, which Mexico had neglected.