From Reason:

During the 20th century, governments murdered over 200 million people. This figure excludes battle deaths from wars. The tables below are from my just-published article Guns Kill People, and Tyrants With Gun Monopolies Kill the Most, 25 Gonzaga Journal of International Law 29 (2021). The data cover 1900 to 1987 and are mainly based on the scholarship of the late University of Hawaii political science professor Rudolph J. Rummel. The few instances in which different figures are used are explained in my article.