So I'm sure people here have heard of the historical phrase known as the hemoclasm of the 20th century. Your challenge is to have as many destructive and more destructive wars, revolutions and the like as possible so
Much that historians in the future say it was the most tragic century in human history
Not allowed: Nuclear war, alien invasion, pandemics that kill most of the population and other assorted mega disasters.
Make it as bloody as destructive as painful as possible.