Last century saw two world wars, followed by the cold war which could have lead to the end of the world. Also a wave of communist revolutions and their aftermath (famines and purges in the Soviet Union, The Great Leap Forward and the Cultural Revolution, the death of a quarter of the population of the world).

I think mismanagement is not accurate. The Soviet system was flawed and inefficient and could not compete. The European empires were made untenable by the world moving on: economic, technological and political changes.

I think Europe and America had a golden age when they were at peace and dominated the world economically from the 80s to this century, and forgot neither of these is a given.