The 20th century was dominated by war and conflict that continually shifted the balance of power around the globe. This pivotal time period saw the emergence of "total wars" like World War I and World War II in which militaries used any means necessary to win—these wars were so massive they encompassed nearly the entire world. Other wars like the Chinese Civil War remained local but still caused the death of millions.
Motives for these wars ranged from expansion disputes to government upsets, even the intentional murder of an entire people. But they all shared one thing: an extraordinary number of deaths. You will notice that in many cases, soldiers were not the only ones dying.nation: The three wars of the 1900s with the highest number of civilian and soldier fatalities were World War II, World War I, and the Russian Civil War, respectively.
World War II
The largest and bloodiest war of the 20th century (and of all time) was World War II. The conflict, which lasted from 1939 to 1945, involved most of the planet. When it was finally over, between 62 and 78 million are estimated to have died.1 Â Of that enormous group, which represents about 3 percent of the entire world population at the time, the huge majority (over 50 million) were civilians.2 Â
World War I
World War I was also catastrophic but total casualties are much harder to calculate as deaths were not well documented. Some sources estimate that there were over 10 million military deaths plus civilian casualties, of which there are thought to be even more (so in total, the number of deaths is estimated at 20 million or more).3  Factoring in the deaths caused by the 1918 influenza epidemic, spread by returning soldiers at the end of World War I, this war's death total is much higher. The epidemic alone was responsible for at least 50 million deaths.4 Â
Russian Civil War
The third bloodiest war of the 20th century was the Russian Civil War. This war caused the death of an estimated 13.5 million people, almost 10% of the population—12 million civilians and 1.5 million soldiers.5  Unlike the two world wars, however, the Russian Civil War did not spread across Europe or beyond. Rather, it was a struggle for power following the Russian Revolution, and it pitted the Bolsheviks, headed by Lenin, against a coalition called the White Army.
Interestingly, the Russian Civil War was over 14 times deadlier than the American Civil War. By comparison, the latter was a much smaller war that resulted in 642,427 Union casualties and 483,026 Confederate casualties.6 Â However, the American Civil War, which began in 1861 and ended in 1865, was by far the deadliest war in history for the United States. The second deadliest in terms of American soldier fatality was World War II with a grand total of 416,800 military deaths.7 Â
Other Major Wars and Conflicts of the 20th Century
Many wars, conflicts, revolutions, and genocides shaped the 20th century outside of these top three largest. Take a look at this chronological list of other major wars of the 20th century to see just how much this century was impacted by battle.
