Bloodletting
WordNet
noun
(1) Indiscriminate slaughter
"A bloodbath took place when the leaders of the plot surrendered"
"Ten days after the bloodletting Hitler gave the action its name"
"The valley is no stranger to bloodshed and murder"
"A huge prison battue was ordered"
(2) Formerly used as a treatment to reduce excess blood (one of the four humors of medieval medicine)