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These Are the 5 Wars That Changed History (And Killed Millions) Forever

Exactly how many people were killed in the various Mongol invasions is difficult to pin down. Historians have likely exaggerated many of the statistics, helped by the Mongols themselves. The Mongols spread word of atrocities far and wide to demoralize those next in line for conquest. Revisionist studies of the Mongol invasions have proposed rolling back the number killed considerably, from roughly 40,000,000 to perhaps “only” 11.5 million during a period of 120 years.

World War I

Sixteen million people were killed in World War. Of those, 9,000,000 were combatants and 7,000,000 were noncombatants.

The high death rate in World War I was a result of several factors. Political demands dictated every square foot of national territory must be held, which necessitated large armies. Militarily, many armies maintained an unflinching attitude towards maintaining the offensive, despite the fact that — for the time being — the defense was stronger than the offense.

World War I was the first Industrial Age war fought on a global scale, introducing machine guns, tanks and artillery on a widespread basis. The machine gun in particular dramatically increased levels of firepower for the infantry—but mostly in the defense.

World War I was marked by several grinding, bloody battles that became infamous for losses incurred on both sides. One of the first was the First Battle of the Marne, which saw French casualties of 250,000. Germany’s casualties are only an estimate but thought to be equal to those of the French.

The First Battle of the Marne, rather than repulsing military and political leaders and forcing them to change tactics, merely set the tone for the rest of the war. The Battle of Verdun cost an estimated 714,000 casualties during a three hundred day period. Total casualties at the Battle of the Somme are thought to be between 700,000 and 1.1 million. Casualties on the Eastern Front were worse, with 300,000 Germans and 2.4 million Russians killed—many due not to not combat but hardship and disease.

World War I was also probably the last time a war with a large death toll claimed more combatant lives than noncombatants. Despite so much of the war being fought on French soil, French civilian deaths are thought to be only 40,000.

World War II

The most lethal war in human history is almost certainly World War II. Other wars may have been more lethal but lack credible records. Sixty to eighty million people died between 1939 and 1945. Twenty one to twenty five million of the deaths were military, the remainder civilian.

The concept of Total War, in which the scope of legitimate wartime targets is extended from the enemy military to the state supporting it, relaxed previous restrictions and made even cities targets. Strategic bombing allowed air forces to drop bombs deep behind enemy lines, and civilian deaths from aerial bombing reached at least one million.

Unlike World War I, World War II was a truly global war with much of the fighting taking place in Asia and the Pacific. The Soviet Union lost an estimated 27 million military personnel and civilians, making it by far the country with the highest death toll. China is thought to have suffered 20 million deaths, Germany 6-7 million, and Japan roughly 2.5 to 3.2 million. The United States was fortunate, losing approximately 420,000, all but 10,000 military deaths.

Further exacerbating the number of civilian casualties was the large amounts of territory occupied by the Axis powers. Germany and Japan were both brutal occupiers, and civilians in countries such as Yugoslavia, the Soviet Union, Poland, China and the Philippines—just to name a few—suffered appallingly.

Acts of genocide contributed significantly to the war’s death toll. Germany’s campaign of extermination against Jews, Slavs, Roma, homosexuals, German dissidents and the disabled claimed an estimated 11 million lives.

Kyle Mizokami is a writer based in San Francisco who has appeared in The Diplomat, Foreign Policy, War is Boring and The Daily Beast. In 2009 he cofounded the defense and security blog Japan Security Watch.