The Cuban Missile Crisis, October 1962. The Cuban Missile Crisis of October 1962 was a direct and dangerous confrontation between the United States and the Soviet Union during the Cold War and was the moment when the two superpowers came closest to nuclear conflict.
1. disease brought by colonists was a major factor. Kills millions
2. violent conflicts between the colonists and/or British forces against the natives
3. The westward expansion (there's a special name for it) Colonists kept colonizing deeper and deeper into the mainland until reaching the western sea coast. killing 10's of thousands on the way there
*millions died, possible around 10 mill
The reason they went to war is when the Athens interfered in Persian affairs.