Settlers moved to the west because they wanted a free start, have more land and more freedom to do whatever they wanted.
Due to the settlers moving to the west Native Americans were killed along with their journey and were forced to move to the west along with the settlers. The settlers also killed oxen along their way to move the Native Americans more to the West.
They were forced to change their religion into catholic, go to church every Sunday, have no slavery etc.
Texas And California were acquired after the U.S. and Mexico war.
People were mad because the states in the south wanted slavery and the states in the north didn't want slavery.