Answer:
The arrival of European in America.
Cultural differences.
Wars.
Step-by-step explanation:
The arrival of European settlers in North America led to the decline and death of Native Indians. Before the arrival of European, the region was inhabitant with Native Indians. European brought diseases which led to the death of thousands of the Natives as they did not have immunity to fight it. The land was another issue which began to arise as settlers began to take it from the Indians for farms and cattle.
The cultural difference also led to hostility among the settlers and Indian tribes. Natives were very much close to mother nature and related to the environment where English and other European were Christians and interested in materialistic, which led to frequent conflict. Settlers considered them to be barbarian as they wore hides and carry primitive tools.
Wars were common as native fought for their rights and land which was taken away from them despite agreeing on several treaties. Thousands of native Indians died in wars. As they began to fail, they forced to flee from their home. Trail of Tears is one such incident where they ordered to leave to settle in reservations.