Says the New York Times, though: After more than four years of fighting, 8.5 million soldiers had been killed, including more than 100,000 Americans, and 7 million civilians were dead. In that time, modern warfare was born, and the trenches of Western Europe became a charnel house*. Just 20 years later World War II would start, bringing vastly greater destruction, and numbers of casualties.
*A building or vault in which corpses or bones are piled.