Bunch of things: • Europeans brought tons of diseases (smallpox, influenza, etc), which changed the way Natives lived by killing them. Some historians estimate that as much as 80% of North America's Native population died in the 200 years after Columbus. • Europeans brought new trade goods and resources, like iron and brass and beads. This changed Native economies and modified the ways they conducted warfare. • Europeans brought horses, which Natives then acquired and quickly mastered. This dramatically changed the balance of power, as tribes who became best at using horses (like the Comanche and Shoshone) rapidly gained power and land at the expense of other tribes.
I'm pretty sure that it is - It allowed people in the territories of Kansas and Nebraska to decide for themselves whether or not to allow slavery within their borders.
