Why did the native americans population decrease in north america and south america after the arrival of the europeans?

Which of the following could affect the human population? a hurricane makes landfall on an uninhabited island.a deadly virus emerges that can pass from human to human.a civil war breaks out in italy.a solar eclipse occurs.

What is one way that the congress of vienna changed the map of europe?

Otto von bismarck once said that a great war might someday be caused by some damed foolish thing in the balkans was he right, explain