Adventurous men who hiked through forests trapping animals and living off the land. Had built many forts and trails.
the mexican american war
Region west of the rocky mountains. Trail which helped many settlers move west.
Mormons in Utah 
religon!
An idea that the united states is destined by god to expand it's territory and it's democracy. Expanded on idea of American expansion.
california gold rush
GOLD!
A war struck out because Americans never accepted to be Mexican. War ended with America gaining more land taking control over California, Arizona, and New mexico. 
Moved to Utah to seek refuge as they were persecuted back in the east. Inspired others to moved west as well.
Many moved to California in hopes of finding gold and becoming rich. Most didn't find any but California had enough people to become a state.