Disease was the biggest killer. The indians didn't have immune systems like the Eurpoeans did, so most of them died especially due smallpox.This is the biological encounter of the Old and New world, and went beyond deadly germs. It included gifts from the Europeans to the Americas (horses, cattle, chickens, wheat, sugar cane, fruits, veggies, etc.) Africans brought rice and yams. Americans also gave a lot too, including corn, potatoes, beans, tomatoes, squash, turkeys, chocolate, etc. The exchange of food products enriched diets and allowed for enormous population growth. There were also people mixing, and interracial births occurred.