Answer:
because it was "one of the deadliest conflicts"
Step-by-step explanation:
"Also called The Great War, World War I was one of the deadliest conflicts in history, and set the stage for another world war just 20 years later. It was known as “The Great War”—a land, air and sea conflict so terrible, it left over 8 million military personnel and 6.6 million civilians dead."