After Spanish Christopher Columbus discovered the new world which today we know as United States Of America (USA), the local population of Red Indian had to suffer the greatest ethnic cleansing and genocide which was carried out of the face of the earth.
It is believed that almost red Indians or indigenous people were killed by the European settlers. It is believed that there were 10 million locals living in the continent when people from west started enslaving them and capturing the land.
After the census in 1900 it was found that only 300,000 Native Americans were alive and living in the continent. The natives were not only killed by the settlers but many died because of diseases epidemic for which red Indians had no acquired impunity. Small and measles killed millions after Europeans settled in these lands.
This is considered one of the worst genocide which is still not accepted as genocide. Numerically more natives were killed by Europeans settlers than Jews who were gas chambered by Hitler.