Recently worse than ever thanks to modern technology.
The evidence from history shows that wars between states are far less deadly than wars involving tribal societies.
This is what tribes do to each other.
http://en.wikipedia.org/wiki/Crow_Creek_massacreThe Crow Creek massacre occurred around 1325 between Indian groups in the South Dakota area.
...
The attacking group slaughtered the people on the bluff. Anthropologists, led by Thomas Emerson, found the remains of 486 people from the attack. Many of these remains had signs of torture and mutilation. These included tongues being cut out, scalping, teeth broken, heads cut off, and other forms of dismemberment.
Or what tribes do to civilizations. Even the Soviets in Russia or Cambodia or the Nazis in Eastern Europe did not rise to this level of total destruction.
http://en.wikipedia.org/wiki/Siege_of_Baghdad_%281258%29
The invasion left Baghdad in a state of total destruction. A number of inhabitants ranging from 100,000 to 1,000,000 were massacred during the invasion of the city, and the city was sacked and burned. Even the libraries of Baghdad, including the House of Wisdom, were not safe from the attacks of the Ilkhanate forces who totally destroyed the libraries, and used the invaluable books to make a passage across Tigris River[citation needed]. As a result Baghdad remained depopulated and in ruins for several centuries, and the event is conventionally regarded as the end of the Islamic Golden Age.
