12 of the Deadliest Wars in World History

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By Douglas A. McIntyre Updated Published
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12 of the Deadliest Wars in World History

© Hulton Archive / Hulton Archive via Getty Images

The war in Ukraine stretches on well into its second year. The conflict, which many pundits expected to end after a few months, has exceeded all but the most conservative estimates, largely because Ukraine’s western allies have funneled tens of billions of dollars in weapons into the besieged nation. A report released last month estimates that as many as 17,500 Ukrainians and 43,000 Russians have been killed since the invasion began. No matter how long the war drags on, the death totals in the war will never close to some of the most horrific in world history, in which millions died.  

To find the wars that killed the most people in history, 24/7 Wall St. reviewed nonprofit The Borgen Project’s list, Top 12 Deadliest Wars in History. All figures are from The Borgen Project.

What is called “modern war” began about the year 1800. It was characterized by the wide use of gunpowder and heavy weapons, which included, in particular, cannons. The earliest of these were the Napoleonic Wars (1803 to 1815). These had another characteristic. They were fought over large geographic areas that included multiple nations.

While the American Revolutionary War (1775 to 1783) was the first war fought on U.S. soil, the total number of combatants killed was about 20,000, and civilian deaths were approximately the same. That total is horrible, but it does not compare at all with the next war fought in the United States. Civil War deaths have been estimated as high as 850,000. (These are the wars in which the most Americans died.)

Most major wars that occurred after the Civil War were fought between two or more countries. Among the exceptions are the Chinese Civil War, which started in 1927 and ran until 1950. It is estimated to have killed 8 million combatants and civilians.

Navies were an early change in how wars were fought. A more recent, but major, change in warfare tactics was the use of aircraft as weapons. Planes were not widely used until World War I and eventually evolved to the point where they could level entire cities, which first happened in World War II.

World War II was fought across virtually all of Europe and much of the Pacific, and a number of armies were involved, including soldiers from India. The war in the Pacific theater ended with the atomic bombs dropped on Hiroshima and Nagasaki, which are estimated to have directly killed 200,000 people, mostly civilian. (These are 18 of the deadliest weapons of all time.)

Click here to see this war killed the most people in history

Brent Stirton / Getty Images News via Getty Images

The Second Congo War
> Years fought: 1998-2003
> Approximate deaths: 5.4 million

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Hulton Archive / Hulton Archive via Getty Images

Napoleonic Wars
> Years fought: 1803-1815
> Approximate deaths: 3.5 million-6 million

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Public Domain / Wikimedia Commons

The Thirty Years’ War
> Years fought: 1618-1648
> Approximate deaths: 8 million

Public Domain / Wikimedia Commons

The Chinese Civil War
> Years fought: 1927-1950
> Approximate deaths: 8 million

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Public Domain / Wikimedia Commons

The Russian Civil War
> Years fought: 1917-1922
> Approximate deaths: 9 million

Public Domain / Wikimedia Commons

The Dungan Revolt
> Years fought: 19th-century China during the Qing Dynasty
> Approximate deaths: 20 million

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Public Domain / Wikimedia Commons

An Lushan Rebellion
> Years fought: 755 A.D.-763 A.D.
> Approximate deaths: 36 million

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Hulton Archive / Hulton Archive via Getty Images

World War I
> Years fought: 1914-1918
> Approximate deaths: 18 million

Henry Guttmann Collection / Hulton Archive via Getty Images

Taiping Rebellion
> Years fought: 1850-1864
> Approximate deaths: 20 million-30 million

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Johann Nieuhoff / Public Domain / Wikimedia Commons

The Qing Dynasty Conquest of the Ming Dynasty
> Years fought: 1618-1683
> Approximate deaths: 25 million

Michael Ochs Archives / Michael Ochs Archives via Getty Images

The Second Sino-Japanese War
> Years fought: 1937-1945
> Approximate deaths: 29 million

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Three Lions / Hulton Archive via Getty Images

World War II
> Years fought: 1939-1945
> Approximate deaths: 70 million

Photo of Douglas A. McIntyre
About the Author Douglas A. McIntyre →

Douglas A. McIntyre is the co-founder, chief executive officer and editor in chief of 24/7 Wall St. and 24/7 Tempo. He has held these jobs since 2006.

McIntyre has written thousands of articles for 24/7 Wall St. He is an expert on corporate finance, the automotive industry, media companies and international finance. He has edited articles on national demographics, sports, personal income and travel.

His work has been quoted or mentioned in The New York Times, The Wall Street Journal, Los Angeles Times, The Washington Post, NBC News, Time, The New Yorker, HuffPost USA Today, Business Insider, Yahoo, AOL, MarketWatch, The Atlantic, Bloomberg, New York Post, Chicago Tribune, Forbes, The Guardian and many other major publications. McIntyre has been a guest on CNBC, the BBC and television and radio stations across the country.

A magna cum laude graduate of Harvard College, McIntyre also was president of The Harvard Advocate. Founded in 1866, the Advocate is the oldest college publication in the United States.

TheStreet.com, Comps.com and Edgar Online are some of the public companies for which McIntyre served on the board of directors. He was a Vicinity Corporation board member when the company was sold to Microsoft in 2002. He served on the audit committees of some of these companies.

McIntyre has been the CEO of FutureSource, a provider of trading terminals and news to commodities and futures traders. He was president of Switchboard, the online phone directory company. He served as chairman and CEO of On2 Technologies, the video compression company that provided video compression software for Adobe’s Flash. Google bought On2 in 2009.

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