The key cause was economic hardship
<span>Social darwinism and laissez faire economics were most closely associated with the interests of big business owners. Big business owners had the most to gain from embracing such tactics. With social darwinism and laissez faire these business owners could prevent the government from trying to regulate them and they could take out rival companies and potentially monopolize whichever market they operated in.</span>
They came to trade fur, they also were looking for new land and a good route to the Pacific, and sought to convert American Indians. :)
Everything except camping and every American owns a car
