There were numerous things that changed in the Americas and its native population after the Europeans arrived, but it was not just the Native Americans that were influenced, the Europeans were affected by some things as well.
One major effect was the spreading of diseases by the Europeans on the Native Americans. This was the prime reason that they started to die out rapidly and almost went extinct.
The Europeans too were affected by the Native American diseases, so they had lot of problems with several problems, such as syphilis, so lot of people died because of it.
Another major influence was the displacement of the Native Americans. The Europeans managed to overpower them and took over their territories, forcing the Native Americans to move westward into new territories where they had to engage in war with other tribes in order to get the land.
