The University of Hawaii has a page dedicated to the study of democide.
What is democide?
Democide: The murder of any person or people by a government, including genocide, politicide, and mass murder.
Let's look at some of the democide statistics from the 20th century...
China (PRC) (1949 – 1987) — 76,702,000 people killed.
USSR (1917 – 1987 ) — 61,911,000 people killed.