Once Europeans arrived, what killed a large number of Native Americans, impacting Native American populations for decades after?

smallpox

Explanation:

the europeans arrived to america with a disease called smallpox and since the indigenous people had never experienced it before, it wiped out 90% of the population

Diseases. The immunity of the Native Americans had not been exposed to the diseases brought by the Europeans. Therefor, their bodies lacked the ability to fight the diseases causing many to die and the diseases spread rapidly. Examples of these diseases were: small pox, influenza, measles, and chicken pox.

Explanation:

b.

jim crow laws were enacted in northern states.