Congo Free State (1885-1908)
Death toll: 8-12 million
As Europe’s great powers divided up Africa, King Leopold II of Belgium grabbed a big slice for himself in the Congo, claiming that he would dispatch missionaries to “civilize” the native tribes.
Instead he looted the area for rubber and ivory, extracted with native labor under threat of death or dismemberment: Anyone who failed to deliver their quota was liable to have a hand chopped off, or worse.
British missionaries and activists eventually spread the word about the horror, leading the great powers to force Leopold to give up the colony – until then, his personal property – to the Belgian government.
This photo of a mutilated laborer was taken by missionaries in order to document the brutality. Wikimedia Commons
Mexican Revolution (1910-1920)
Death toll: 1-2 million
The multi-sided Mexican Revolution and civil war pitted different factions of the elite against each other as well as peasant revolutionaries.
The United States became involved in 1916 after Pancho Villa (pictured, at an insurgent camp in 1915), a rebel general, conducted cross-border raids killing scores of Americans.
Ultimately, the conflict resulted in The Mexican Constitution of 1917, which remains in place to this day.Wikimedia Commons
World War I (1914-1918)
Death toll: 18 million
After the assassination of the Archduke Franz Ferdinand in 1914, Austria-Hungary decided to crush the kingdom of Serbia once and for all, but things didn’t go as planned, and soon Austria-Hungary and its ally Germany were at war with Serbia’s protector Russia, Russia’s ally France, and France’s ally Britain.
Later Italy and the Ottoman Empire joined in, but nobody was able to break through the bloody stalemate of trench warfare.
German submarine attacks provoked the United States to declare war in April 1917, and American manpower finally helped turn the tide on the Western Front in 1918.
However, the unfair Versailles Treaty that ended the war left the losing side, Germany, nursing a grudge, ultimately leading to World War II.
World War I also saw the first major genocide of the 20th century, when the Ottoman government murdered approximately 1.5 million Armenians.
Pictured: Australian soldiers walk through the Chateau Wood near Ypres, Belgium in 1917.Wikimedia Commons
Russian Civil War (1917-1923)
Death toll: 9 million
World War I sparked revolution and civil war in Russia, pitting the communist "Reds" against "the Whites," a loose coalition of anti-communist forces.
Much of the fighting took place along railroad lines with armored trains, and disruption to transportation networks caused mass starvation (pictured: hungry orphans living on the street).
Eventually, the fighting ended with the triumph of the Reds and the formation of the Soviet Union.Wikimedia Commons
Spanish Flu (1918-1920)
Death toll: 20-50 million
It’s still unclear where the flu actually started, with possible origins in Asia, Mexico, South Africa, and the United States (the flu didn’t actually originate in Spain, but was simply better documented there because Spain, a neutral country, didn’t have wartime press censorship).
The global influenza pandemic of 1918-1920 was probably caused or intensified by World War I, which brought both unprecedented global movements of people and health crises due to food shortages and other diseases.
The flu pandemic came in three distinct waves, peaking in late 1918, when it killed around 25 out of every 1,000 people infected. Wikimedia Commons
Russian Famine (1921-22)
Death toll: 5 million
After winning the Russian Civil War, Vladimir Lenin’s Bolsheviks set out to remake Russia as a socialist paradise, but it didn’t quite turn out that way. The chaos of the recent civil war, plus mass requisitions of food by the Bolsheviks and a natural famine resulting from drought, killed millions, forcing some to resort to cannibalism (pictured).Wikimedia Commons
Chinese Famine (1928-30)
Death toll: 3-6 million
One of many episodes of mass starvation throughout Chinese history, the natural drought and famine of 1928-1930 was exacerbated by the disruptions of China's "Warlord Era," during which several military regimes ruled over various pprts over the nation.
Pictured: starving mother and child refugees from Shandong. 1930.Topical Press Agency/Getty Images
Chinese Floods (1931)
Death toll: 3.7 million
After the drought of the late 1920s, the surprising return of heavy rains and snow caused massive flooding along the Yangtze and Huai River basins. In Hankou, the floodwaters reached a level of 53 feet above flood stage.
Pictured: Boats navigating flood waters in Hankou (now part of Wuhan) in central China. September 1931.Culture Club/Getty Images
Stalin’s Purges And Industrialization (1931-1953)
Death toll: 20 million
In 1931, Soviet leader Joseph Stalin was determined to finish Vladimir Lenin’s work by industrializing the Soviet Union to bring it up to the level of the world's leading capitalist countries. What followed was a crash course of top-down development financed in part by the sale of grain to capitalist Western countries, resulting in the starvation of at least 2.4 million people in the Ukraine.
Meanwhile, endless political purges prevented anyone from growing powerful enough to challenge Stalin’s hold on power. His henchmen also murdered around 20,000 Polish military officers and intellectuals after dividing Poland with Hitler in 1939 (pictured: the Katyn massacre of Polish nationals, 1940).Wikimedia Commons
Spanish Civil War (1936-1939)
Death toll: 500,000
In 1936, Spain became the latest battleground between communist and anti-communist forces, pitting Republican fighters supported by the Soviet Union (not all of them communists) against General Francisco Franco's fascists, who ultimately triumphed.Fox Photos/Getty Images
World War II (1939-1945; In Asia: 1931-1945)
Death toll: 50-80 million
The deadliest cataclysm in human history saw the Axis of Nazi Germany, fascist Italy, and Imperial Japan stake everything on a bid for world domination, and lose.
At the same time that unprecedented numbers of troops took the battlefield, Axis powers carried out programs of genocide against civilian populations. The extreme racism of the Nazi ideology resulted in the deaths of some 6 million Jews along with five million other “undesirables” during the Holocaust. In Asia, the Japanese killed between 15 and 20 million Chinese citizens starting in 1931 with the Japanese invasion of Manchuria, along with millions more in other occupied countries.
Pictured: Dresden, Germany after the Allied firebombing on February 13-15, 1945.Wikimedia Commons
Henan Famine (1942-43)
Death toll: 2-3 million
Once again, natural causes conspired with the disruption of war. This time, the Japanese invasion of China as part of World War II helped cause mass starvation there, with drought making things worse.
Pictured: A child lies down on the sidewalk, too exhausted and sick to feed himself.George Silk/The LIFE Picture Collection/Getty Images
India-Pakistan Partition (1947)
Death toll: 1-2 million
During the colonial period, India's British rulers were happy to exploit longstanding tensions between Muslims against Hindus, using "divide and rule" tactics to keep the population submissive. As British rule drew to an end, these tensions erupted in mass rioting and massacres, reaching a climax in the partition of majority-Hindu India and majority-Muslim Pakistan in 1947.
Pictured: Vultures feeding on corpses lying abandoned in an alleyway after bloody rioting between Hindus and Muslims. Circa 1946.Margaret Bourke-White/The LIFE Picture Collection/Getty Images
Chinese Civil War (1927-1937, resumed 1945-1949)
Death toll: 8 million
This decades-long conflict pitted China's republican government against a communist insurgency. The conflict began in 1927, and after a pause to fight the Japanese in the 1930s and 1940s, the bloodiest phase of the war resumed in 1945, which saw the nationalists under Chiang Kai-shek and the communists under Mao Zedong face off. The latter emerged victorious and the defeated nationalists fled to Taiwan in 1949.
Pictured: Communist forces capture the Lanzhou Yellow River bridge on August 26, 1949.Wikimedia Commons
Korean War (1950-1953)
Death toll: 3.5 million
A civil war pitting communists against anti-communists, the Korean War was also a proxy struggle of the Cold War, as the West backed South Korea against Marxist North Korea, supported by the USSR and China. The conflict ended with a military stalemate and the division of the peninsula into the sovereign states of North and South, causing animosities that persist to this day.
br>Pictured: A grief-stricken American infantryman whose buddy has been killed in action is comforted by another soldier. In the background a corpsman methodically fills out casualty tags. Haktong-ni area. August 28, 1950.Wikimedia Commons
Asian Flu (1957-1958)
Death toll: 1-2 million
Although not nearly as deadly as the Spanish flu of 1918-1920, the Asian flu of 1957-1958 moved from Asia to Europe and the U.S., hitting young people especially hard and prompting the first efforts to begin mass production of vaccines before the disease hit epidemic proportions.
Pictured: A Swedish classroom with most of the class out sick due to the flu.Wikimedia Commons
Great Leap Forward (1958-1962)
Death toll: 20-45 million
After the communist victory in the Chinese Civil War in 1949, leader Mao Zedong was determined to drag his country into the future. This meant remaking a rural society into an industrial powerhouse, while skipping all the steps in between – and in Mao’s doctrinaire mind, development boiled down to producing lots of steel.
So, across China, rural communes gave up producing food to forge steel in jerry-rigged furnaces, while other communes worked “overtime” to produce more food to feed them. The result was mass starvation and a bunch of useless steel nuggets.
Pictured: Peasants in Xinyang show their zeal farming under floodlights. 1959.Wikimedia Commons
Vietnam War (1954-1975)
Death toll: 1.4-3.6 million
Originally a nationalist struggle against French colonial rule, the Vietnam War became yet another proxy fight in the Cold War, with communist North Vietnam supported by the Soviet Union and South Vietnam supported by the U.S. and other Western powers. In the end, the North's forces emerged victorious and reunited the country under communist rule.
Pictured: Thich Quang Duc, a Buddhist monk, burns himself to death on a Saigon street to protest alleged persecution of Buddhists by the South Vietnamese government. June 11, 1963.Wikimedia Commons
Indonesian Massacres (1965-1966)
Death toll: 500,000-2 million
After an attempted communist coup in 1965, Indonesia became another Cold War battleground with government-backed massacres targeting communists, as well as ethnic Chinese and various political dissidents. The disorder resulted in the dictatorship of the anti-communist, U.S.-backed General Suharto from 1967-1998.
Pictured: A sword-like knife used to kill communists, called a parang, being thrown by a young college student.Co Rentmeester/The LIFE Picture Collection/Getty Images
Cultural Revolution (1966-1976)
Death toll: 2 million
After being discredited and sidelined for the disaster of the Great Leap Forward, Chinese leader Mao Zedong was determined to take back absolute power from more moderate communists, and turned to a new generation of younger Chinese as his allies. Building up a cult of personality, Mao encouraged the "Red Guards" to persecute the older Chinese revolutionaries and tear down the country's traditional Confucian culture. Order was finally restored after Mao died in 1976.
Pictured: Red Guards strike a dramatic pose.Universal History Archive/UIG via Getty Images
Nigerian Civil War (1967-1970)
Death toll: 500,000-2 million
An ethnic and tribal conflict, the Nigerian Civil War saw the province of Biafra try to break away from the rest of the country — and ultimately fail.
It was an unusual Cold War conflict because the USSR and Britain both supported the Nigerian government, while France and other countries supported the Biafrans and other European mercenaries also played a prominent role as well.
Pictured: Two foreign hostages under guard by Nigerian federal troops in Port Harcourt in 1968.Terry Fincher/Express/Getty Images
Hong Kong Flu (1968-1969)
Death toll: 1 million
Named for the city where it was first identified, the Hong Kong flu spread quickly because of new global transportation systems.
Pictured: An American couple looks at a public health billboard in Des Moines, Iowa.Bettmann/Contributor/Getty Images
Bangladesh War Of Independence (1971)
Death toll: 3 million
Upon the partition of India and Pakistan in 1947, the latter originally included most of the former colony's Muslim territories, in West Pakistan (now just Pakistan) and East Pakistan (now Bangladesh). However, long-simmering ethnic and nationalist tensions erupted after the government's incompetent response to the 1970 Bhola Cyclone, which killed at least 300,000 people. A bloody civil war then broke out, and Indian intervention ultimately helped secure Bangladesh's independence.
Pictured: An advertisement for a George Harrison record meant to raise funds and awareness in the name of the war.Wikimedia Commons
Ethiopian Civil War (1974-1991)
Death toll: 500,000-1.5 million
Yet another Cold War proxy fight, the Ethiopian Civil War began in 1974 when the Marxist Derg overthrew the country's monarch, Emperor Haile Selassie with support from the USSR and Cuba. A famine made worse by the war killed another million people. The war finally ended in 1991 with the overthrow of the communist regime of Mengitsu Haile Mariam.
Pictured: Defeated and injured Ethiopian soldiers after the 1991 overthrow.Wendy Stone/Corbis via Getty Images
Cambodian Genocide (1975-1979)
Death toll: 1.5-3 million
In the 1970s, the chaos created by the Vietnam War spilled over into neighboring countries. In Cambodia, the Khmer Rouge communists set out to remake the small country as an agrarian utopia by uprooting city dwellers and killing those deemed to be "intellectuals" or "foreign sympathizers," which in practice meant anyone who, for example, wore glasses or spoke a foreign language.
The Khmer Rouge stayed in power after the genocide, and remained there into the 1990s.
Skulls lie in the killing fields of Choeung Ek. 1981.Roland Neveu/LightRocket via Getty Images
Angolan Civil War (1975-2002)
Death toll: 500,000
Following Angola's independence from Portugal, it was torn apart by a Cold War struggle between Maoist rebels in UNITA, backed by the USSR and Cuba, and the central government backed by the U.S. and other Western powers. As is so often the case in Africa, the supposedly ideological struggle was often a fight for control of natural resources including diamonds and oil. And as is also so often the case in African wars, child soldiers were common.
Pictured: Angolan children in a military parade. 1976.Keystone/Getty Images
Soviet-Afghan War And The Afghan Civil War (1979-1992)
Death toll: 500,000-2 million
One of the Cold War's "hot wars," the conflict began when the Soviet Union invaded Afghanistan to back a puppet government threatened by a coup plot, orchestrated with CIA support, in 1979. The U.S. helped create an Islamist insurgency of fighters, or mujahideen, to wage a proxy war against the Soviet invaders, supplying them with Stinger missiles that helped paralyze the Soviet helicopter fleet.
Following the Soviet withdrawal in 1989, civil war continued with the mujahideen eventually emerging victorious.
A wounded mujahideen fighter reaches out for help. 1989.David Stewart-Smith/Getty Images
Iran-Iraq War (1980-1988)
Death toll: 1.5 million
In 1980 Saddam Hussein's Iraq invaded neighboring Iran in a bid to conquer oil-rich border territories, but fighting soon devolved into World War I-style trench warfare, complete with poison gas and human wave attacks. Iraq received financial support from the U.S., which also helped procure weapons for the Iraqis, perhaps in retribution for the Iran hostage crisis.
In the end, both countries were left with a military stalemate and no significant territory having changed hands.
Pictured: Basij (mobilized volunteer forces) women in black chador carry rocket launchers.Kaveh Kazemi/Getty Images
Death toll: 35 million
There is still disagreement about where the human immunodeficiency virus originated. One theory holds that the two main strains of the virus actually crossed over from chimpanzees or monkeys to human beings in west central Africa on several different occasions, the first sometime prior to 1931, perhaps when people ate “bush meat” infected with a strain of the simian immunodeficiency virus.
Then, it may have spread via global transportation networks: sailors may have brought the disease from Africa to Haiti in the 1950s or 1960s, and then the U.S. It was first identified in the U.S. among gay men in big cities in the early 1980s.
Anti-retroviral drugs debuted in the 1990s, radically changing the prognosis for patients and helping to bring the epidemic under control, despite the fact that it still claims disproportionate amounts of lives in the world's poorer, less-developed regions, namely in Africa.
Pictured: The AIDS Memorial Quilt in Washington, D.C.Wikimedia Commons
Somali Civil War, 1991-present. Death toll: 500,000
Divided into several territories during the colonial period, Somalia fell apart in 1991 as various rebel groups vied for power, and joined in more recent years by Al-Shabab, an Islamist militia and terrorist group.
Nevertheless, some parts of the country are actually relatively peaceful: Somaliland in the north, for example, has functioned more or less independently for several decades.
Pictured: A young fighter from the Al-Shabab militia shows the wound in his hand which he suffered while battling Somali government forces in 2009.MOHAMED DAHIR/AFP/Getty Images
Rwandan Genocide (1994)
Death toll: 500,000-1 million
In just a few months in 1994, in the midst of a civil war in Rwanda, the country's ethnic Hutu majority government incited Hutus to murder their Tutsi countrymen, ultimately wiping out about 70 percent of the country's Tutsi population before the Tutsi Rwandan Patriotic Front, a rebel army led by Paul Kagame, put an end to the slaughter. Much of the killing was carried out with machetes and other simple weapons.
Pictured: A local child stands in a church where a massacre took place in Ntarama, Rwanda. September 16, 1994.Scott Peterson/Liaison/Getty Images
North Korean Famine (1994-1998)
Death toll: 600,000-2.5 million
Faced with a famine brought on by factors including drought and loss of Soviet support, the totalitarian government of communist North Korea allowed several million of its citizens to starve to death before foreign aid arranged by its archenemy, South Korea, ended the crisis.
Pictured: Arid North Korean farmland and orchards. 1995.Ben Davies/LightRocket via Getty Images
Second Congo War (1998-2003)
Death toll: 3-5.4 million
Sometimes called "Africa's World War," the Second Congo Civil War began after Rwanda intervened in eastern Congo to counter a threat from Hutu militias based there.
In the First Congo War, the Rwandan-backed Tutsi militias, led by Laurent Desire Kabila, overthrew the regime of Mobutu Sese Seko.
The Second Congo War began after Kabila (and later his son and successor Joseph) turned his back on his former Rwandan backers; the conflict eventually sucked in countries from across Africa, and although diplomacy ended the war in 2003, fighting continues in the north Kivu region.
Pictured: A Tutsi child soldier at play with an AK-47 during the First Congo War.ABDELHAK SENNA/AFP/Getty Images
Syrian Civil War (2011-present)
Death toll: 200,000-500,000
After the initial promise of the Arab Spring in 2011 turned sour, civil wars broke out across the Middle East, with the fiercest fighting taking place in Syria. The multi-sided struggle includes the Syrian government under Bashar al-Assad, multiple rebel groups (some secular, some Islamist), the Islamist terrorist group ISIS, ethnic Kurdish militias, and foreign intervention from Russia, the U.S., and other Western countries.
With no end is in sight, millions more have fled to neighboring countries and Europe.
Pictured: A Syrian man carries a wounded child following an air strike by government forces in Douma. August 2015.SAMEER AL-DOUMY/AFP/Getty Images