An estimated 20 million people were killed in World War 1, 60 to 80 million in World War 2, and between 10 million and 30 million in World War 3 ("Cold War") proxy wars and conflicts.

World War 1 (1914–1918)
Total Deaths: ~20 million
Military: ~9 to 11 million
Civilians: ~7 to 13 million

World War 2 (1939–1945)
Total Deaths: ~60 to 80 million
Military: ~20 to 25 million
Civilians: ~40 to 55 million

World War 3, "Cold War" (1947–1991)
Total Deaths: Highly debated, ranging from 10 million to 30 million.
Because the superpowers did not fight directly, these deaths occurred in major proxy wars and related internal conflicts.

For deeper breakdowns, casualties in major proxy conflicts included:
Korean War (1950–1953): ~3 to 4 million total deaths (mostly civilians and Chinese/Korean troops).
Vietnam War (1955–1975): ~1.3 to 3.8 million deaths, including over 600,000 civilians.