Why were native Americans experiencing their own dark ages

War and violence. While epidemic disease was by far the leading cause of the population decline of the American indigenous peoples after 1492, there were other contributing factors, all of them related to European contact and colonization. One of these factors was warfare.

answer: i think it might be the last one

explanation:

i believe the correct answer is option b. most eastern european nations joined nato.

though i could be wrong, option d. the eastern european nations were granted complete independence, would be another choice.

hope this ! : )