World War I was the deadliest war in history

Explanation

The deadliest war in history was World War II with an estimated 70 to 85 million total deaths between 1939 and 1945, which is aroubd 3% of the global population at the time (roughly 2.3 billion people). World War I (1914 - 1918), on the other hand, caused approximately 15 - 22 million deaths.