Answer: Manifest Destiny, Land and the Idea of Riches
Explanation: During the major rush westward many Americans believed in Manifest Destiny, or the belief that it was god's intention for the United States to reach to the Pacific Ocean. On top of this, congress passed the Homestead Act in 1862, that proclaimed that any individual who had not taken up arms against the United States(note that this was during the Civil War) could claim 160 acres as long as said individual promised to farm it. This caused massive relocation westward, as people sought to build new lives. Finally, the idea of riches. Gold was first discovered in California in 1848, and soon, everyone believed that they could be the lucky individual to find more. Thousands rushed out to the western most parts of the United States trying to win the 1800s lottery, and took their families with them. While many didn't find any, some became very rich from their searches.