The prehistoric people were cavemen
In my opinion the arms race and the existence of theatomic/hydrogen bomb forced the Soviet Union and the United States to fight
"proxy wars" (influencing others to fight, but not directly fighting themselves) because they feared the retaliation of the proxy wars
Beginning in 1873, a series of Supreme Court decisions limited the scope of Reconstruction-era laws and federal support for the so-called Reconstruction Amendments, particularly the 14th and 15th, which gave African Americans the status of citizenship and the protection of the Constitution, including the all-important right to vote. Bill, passed by Radical Republicans in Congress in 1867, that treated Southern states as divided territories. Sometimes called the Military Reconstruction Act or the Reconstruction Act, the First Reconstruction Act divided the South into five districts, each governed by martial law. It was the first of a series of harsher bills that the Radicals passed that year.
It could be increased greenhouse gas effect.
