12. Yellow Turban Rebellion, China, 184-205 AD 3-7 million
Seven million deaths is a horrifying statistic now, but imagine how bad it would have been around 200AD. Think of how small the world's population was then, and how devastating to a single nation a loss of 7 million lives would have been. That was around 3% of the world's population that died in the rebellion, which was part of the Three Kingdoms War. It was a peasant revolt against the Han Dynasty, percolated by famine, loss of land through flooding, and rich landowners paying tiny wages to the massive surplus of workers attempting to find jobs to feed their family. The war was devastating to both sides, and left the state in a horrible condition.