As shown in the graph.
Did the Allied Powers or the Central Power suffered the most casualties?

total number of combatants killed 9 million
total number of soldiers wounded 21 million
civilians dead from disease, hunger, and other war-related causes possibly 9 million
Germany and Russia (casualties) 3.4 million
French males between 25 and 35 dead or wounded nearly half
Britain and its empire (casualties) 1 million

Austria-Hungary (casualties) more than a million
Italy (casualties) more than a half a million
Ottoman Turks (casualties) possibly 325,000
United States (casualties) almost 120,000