Genghiz Khan killed an estimated 40 million people in his conquests, which would have been about 10% of the world's population at that time.

Answer from juestplayer on reddit.com
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Wikipedia
en.wikipedia.org › wiki › List_of_wars_by_death_toll
List of wars by death toll - Wikipedia
2 days ago - Consequently, it excludes mass death events such as human sacrifices, ethnic cleansing operations, and acts of state terrorism or political repression during peacetime or in contexts unrelated to war. ... ^ Some examples would include Operation Condor (60,000–80,000 killed), the Cultural Revolution (1–20 million ...
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Our World in Data
ourworldindata.org › war-and-peace
War and Peace - Our World in Data
March 20, 2024 - This is because the big wars were much more deadly: wars like the Russian Civil War and the Korean War killed several hundred thousand people. And wars such as the Chinese Civil War and the Vietnam War killed between 1 and 2 million combatants. But the deaths in the World Wars loom even over ...
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The Borgen Project
borgenproject.org › home › the blog › top 12 most deadliest wars in history
Top 12 Most Deadliest Wars in History - The Borgen Project
December 14, 2024 - The Dungan Revolt The Dungan Revolt was a war fought between the Hans (Chinese ethnic group native to East Asia) and the Huis (Chinese Muslims) in 19th-century China during the Qing Dynasty. There were approximately 20 million war-related deaths, mostly caused by famine and migration brought ...
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Britannica
britannica.com › world history › wars, battles & armed conflicts
8 Deadliest Wars of the 21st Century | Britannica
June 13, 2025 - In 2015 Russia, a longtime supporter ... of the war. Cease-fire agreements failed to stop the violence, and by 2016 it was estimated that 1 in 10 Syrians had been killed or wounded by the fighting. Four million people fled the country, while millions more were internally displaced. At least 470,000 deaths were caused ...
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Statista
statista.com › statistics › 1009819 › total-us-military-fatalities-in-american-wars-1775-present
United States: war fatalities1775-2024 | Statista
In terms of the number of deaths per day, the American Civil War is still at the top, with an average of 425 deaths per day, while the First and Second World Wars have averages of roughly 100 and 200 fatalities per day respectively. Technically, the costliest battle in U.S. military history ...
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Reddit
reddit.com › r/history › what are the deadliest wars in history as percentage of the world population?
r/history on Reddit: What are the deadliest wars in history as percentage of the world population?

Genghiz Khan killed an estimated 40 million people in his conquests, which would have been about 10% of the world's population at that time.

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Wikipedia
en.wikipedia.org › wiki › World_War_II_casualties
World War II casualties - Wikipedia
1 day ago - The Overmans study did not include Soviet citizens in German service. The details of the Overmans study are presented in German casualties in World War II. In a separate study, Overmans concluded that the actual death toll of German POWs was about 1.1 million men (including 1.0 million in the USSR).
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Fandom
military-history.fandom.com › wiki › List_of_wars_by_death_toll
List of wars by death toll | Military Wiki | Fandom
See also: List of genocides by death toll This list of wars by death toll includes death toll estimates of all deaths that are either directly or indirectly caused by war. These numbers usually include both the deaths of military personnel which are the direct results of battle or other military ...
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Umd
cissm.umd.edu › research-impact › publications › deaths-wars-and-conflicts-20th-century
Deaths in Wars and Conflicts in the 20th Century | Center for International and Security Studies at Maryland
- An itemized total sum of deaths in wars and conflicts "killed or allowed to die by human decision" of approximately 231 million for the 100 years of the 20th Century. The separate components of this sum are provided.
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Our World in Data
ourworldindata.org › conflict-deaths-breakdown
Millions have died in conflicts since the Cold War; most of them in Africa and intrastate conflicts - Our World in Data
July 15, 2024 - And one-sided violence and interstate ... deaths, with about one in twenty deaths each. Intrastate conflicts dominated Asia and Oceania even more, accounting for nearly 90% of conflict deaths between 1989 and 2024. Afghanistan was most affected, experiencing several wars over the decades. One-sided violence claimed most of the other deaths, making up almost one in ten deaths, while deaths in non-state and interstate conflicts were rare, resulting in around 3% and 1% of ...
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Harvard Magazine
harvardmagazine.com › 2001 › 05 › the-deadliest-war-html
The Deadliest War | Harvard Magazine
March 1, 2024 - Drew Faust speaks on how the Civil War’s astounding death toll reshaped American society.
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Wikipedia
en.wikipedia.org › wiki › United_States_military_casualties_of_war
United States military casualties of war - Wikipedia
6 days ago - Because of incomplete records, ... was still about 1,000 too low. Military historian John Shy subsequently estimated the total killed in action at 8,000, and argued that the number of wounded was probably far higher, about 25,000. The "other" deaths are primarily from disease, ...
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American Battlefield Trust
battlefields.org › learn › articles › civil-war-casualties
Civil War Casualties | American Battlefield Trust
Given the relatively complete preservation of Northern records, Fry's examination of Union deaths is far more accurate than his work in the South. Note the mortal threat that soldiers faced from disease. ... There were an estimated 1.5 million casualties reported during the Civil War.
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Reddit
reddit.com › r/optimistsunite › deaths in wars globally going back to 1800
r/OptimistsUnite on Reddit: Deaths in wars globally going back to 1800

This would be even more interesting to see as military conflict deaths relative to global population. Basically, conflict deaths per 10,000 people globally on the y-axis, and year on the x-axis. I imagine the difference would be even more striking, especially visualizing the peace that has been the post-WWII era.

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Our World in Data
ourworldindata.org › grapher › deaths-in-armed-conflicts-by-type
Deaths in armed conflicts - Our World in Data
Included are deaths of combatants and civilians due to fighting in interstate, intrastate, extrasystemic, non-state conflicts, and one-sided violence that were ongoing that year.
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Global Research
globalresearch.ca › usa-us-post-911-wars-caused-4-5-million-deaths › 5893215
America's Post-9/11 Wars Have Triggered 4.5 Million Deaths, Displaced 38-60 Million People, Study Shows - Global ResearchGlobal Research - Centre for Research on Globalization
3 weeks ago - The Brown University studies are ... the death tolls of post-9/11 US wars. A 2015 report by the Nobel Prize-winning group International Physicians for the Prevention of Nuclear War (IPPNW) concluded that 13 years of Washington’s so-called “War on Terror” caused a total of 1.3 million deaths, including ...
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Brown University
watson.brown.edu › costsofwar › costs › human › civilians
Civilians Killed & Displaced | Costs of War | Brown University
Over the course of the post-9/11 wars, over 38 million people in from Afghanistan, Iraq, Pakistan, Yemen, Somalia, the Philippines, Libya, and Syria were displaced, either abroad or within their own countries. Being internally displaced by war is associated with higher rates of indirect deaths. As of August 2021, since the start of the post-9/11 wars, at least 5.9 million Afghans had fled the country or been internally displaced. As of March 2023, more than 1...
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Reddit
reddit.com › r/history › which wars were the deadliest in terms of casualties or deaths per soldier per year?
r/history on Reddit: Which wars were the deadliest in terms of casualties or deaths per soldier per year?

World War 2 was by far the worst in regards to civilian deaths due to the total wars brought upon civilians. Battlefield deaths the American Civil War and WW1 was the worst in regard to old military battle tactics with advanced weaponry.