Extracted from Wikipedia

The Top 10 for each subcategory of deaths caused by humans

War and military action

These figures include deaths of civilians from diseases, famine, and atrocities as well as deaths of soldiers in battle.

1. 62,000,000 – World War II (1937–1945), (see World War II casualties)
2. 36,000,000 – An Lushan Rebellion (756–763)
3. 30,000,000–60,000,000 – Mongol Conquests (13th century)
4. 25,000,000 – Manchu Conquest of Ming China (1616–1644)
5. 20,000,000–50,000,000 – Taiping Rebellion (1851–1864)
6. 17,000,000 – Timur Lenk’s conquests (1370–1405)
7. 15,000,000–66,000,000 – World War I (1914–1918) (see World War I casualties) note that the larger number includes Spanish flu deaths
8. 10,000,000-25,000,000 – Second Sino-Japanese War (1931–1945)
9. 5,000,000–9,000,000 – Russian Civil War (1917–1921)
10. 3,800,000 – Second Congo War (1998–2004)

Individual battles and sieges

1. 2,000,000 – Brusilov Offensive (4 June-20 September 1916)
2. 1,800,000 – Battle of Stalingrad (1942–1943)
3. 1,500,000 – Siege of Leningrad (1941–1944)
4. 700,000 – Battle of Moscow (1941–1942)
5. 500,000 – Battle of Smolensk (1941)
6. 400,000 – Battle of Kiev (1941)
7. 370,000 – Battle of Voronezh (1942)
8. 370,000 – Battle of Belarus (1941)
9. 330,000 – First Battle of the Marne (1914)
10. 300,000 – Battle of the Somme (1916 )

Genocide and democide

1. 40,000,000, contradictory – Mao Zedong’s Regime (China, 1949-1975)[1].
2. 20,000,000–62,000,000 – Stalin’s regime (1924-53), (not including WWII)[2]. (some claim as little as 6,000,000 with 25,000,000 or so being the generally accepted number)
3. 11,000,000–19,000,000 – Slave trade in Islamic World over 1200 years (7th – 19th century) -needs explanation
4. 6,000,000–60,000,000 – African and Atlantic slave trade (16th – 19th century)
5. 5,000,000–12,000,000 – Nazi internments and Holocaust in Europe
• 6,000,000 – Jews
• 3,000,000 – victims of camps of other nationalities, mostly Eastern European
• 2,600,000–4,000,000 Soviet prisoners of war
• 1,000,000+ – Political prisoners
• 500,000-600,000 – Jasenovac concentration camp in Croatia
• 250,000–1,000,000 Roma
• 70,000–275,000 Disabled
• 10,000–220,000 Homosexuals
6. 5,000,000–10,000,000 – Congo Free State, (1877 – 1908)
7. 2,000,000–100,000,000 – Destruction of Native Americans (after 1492) The estimates involved are controversial. For details of the controversy, see the linked article.
8. 2,000,000–3,000,000 – Pol Pot’s communization program (Cambodia, 1975-1979)
9. 1,000,000–3,000,000 Armenian Massacres (1895-1923) Heavily Disputed. Most cited number is 1.5 million.
• 30,000–300,000 – Hamidian (First Armenian) Massacre (1895-1896)
• 6,000–30,000 – 1909
• 600,000–2,000,000 – Second Armenian Massacre (1915-1918)
• 250,000–500,0000 – (1919-1923)
10. 937,000 – Genocide in Rwanda (Rwanda, 1994)

Individual massacres, air raids, and concentration camps

1. 1,100,000 – Auschwitz concentration camp (Oświęcim, Poland, 1940-1945)
2. 700,000-1,000,000 – Treblinka extermination camp, (Treblinka, Poland, 1942-1943)
3. 500,000-900,000 – 1938 Huang He flood, caused by sabotage in the Second Sino-Japanese War (1938)
4. 260,000 – Sobibór extermination camp
5. 250,000–800,000 – Sack of Baghdad by Hulagu Khan (1258)
6. 220,000 – Massacre of the Helvetii (58 BC)
7. 200,000+ – Sack of Moscow by Crimean Tatars, 1571
8. 100,000–300,000 – Jews massacred in Poland by the Cossacks led by Chmielnitzki, (1648 – 1649)
9. 100,000 – Massacre of Romans by Mithridates VI Eupator (Anatolia, 88 BC)
10. 100,000-300,000 Tokyo firebombing,1945

Terrorism

Not all terrorist acts have been accounted for. Just well known ones.

1. 2,994 – September 11, 2001 attacks, (New York City, Arlington, VA, Shanksville, PA, United States, 2001)
2. 344 – Beslan School Siege, (Beslan, Russia, 2004)
3. 329 – Air India Flight 182 (Atlantic Ocean, south of Ireland, 1985)
4. 299 – US and French barracks bombings, (Beirut, Lebanon, 1983)
5. 270 – Pan Am Flight 103, (Lockerbie, Scotland, 1988)
6. 257 – 1993 Mumbai bombings (Mumbai, India, 1993)
7. 225 – 1998 U.S. embassy bombings, (Tanzania, Kenya, 1998)
8. 202 – 2002 Bali bombing, (Indonesia, 2002)
9. 191 – 11 March 2004 Madrid train bombings, (Spain, 2004)
10. 181 – Kerbala and Baghdad attacks, (2004, see Ashoura Massacre)

Murder (by individuals, other than through terrorism)

1. ~650 – Erzsébet Báthory, Kingdom of Hungary, (c.1585 – 1610) – total disputed
2. 400 – Abadan theater arson (Abadan, Iran, 1978)
3. 323 – Circus arson, (Niterói, Brazil, 1961)
4. 300+ – Pedro Lopez, Colombia, Peru, Ecuador, (1969 – 1980) – total disputed
5. ~250 – Dr. Harold Shipman, Hyde, United Kingdom, (1970s?-1998)
6. 198 – Subway arson (Daegu, South Korea, 2003)
7. 140 – Luis Garavito, Colombia, (1992-1998)
8. 125 – Behram, Thugee cult, India, (1790 – 1830)
9. 100 – Donald Henry “Pee Wee” Gaskins, serial killer from Johnsonville, South Carolina who prior to his execution, claimed over 100 killed
10. 97 – Dupont Plaza Hotel arson, San Juan, Puerto Rico, 1986)

Human sacrifice and mass suicide

1. 80,000 (estimated) – suicides of Japanese civilians during the Battle of Okinawa, (1945)
2. 15,000 (estimated) – Holy Inquisition (Europe). 1184 – 1800
3. 8,000 – suicides of Japanese civilians and troops during the Battle of Saipan, (1944)
4. 3,000 (modern estimate) – 80,000 (‘classic’ estimate) – temple of Huitzilopochtli, Tenochtitlan
5. 960 – Jewish zealots, after a prolonged siege of Masada, during the Roman-Jewish war of 66-73
6. 913 – Jonestown mass suicide & murders (Guyana, 1978)
7. 53 – Order of the Solar Temple (Switzerland and Canada; October 5, 1994)
8. 39 – Heaven’s Gate (California, 1997)
9. 16 – Order of the Solar Temple (France; December 23, 1995)

Riot or political demonstration

1. 87,000 – Chinese massacres of Tibetan pro-independence protestors (Tibet, China 1959)
2. 30,000 – Nika riots (Constantinople, 532)
3. 30,000 – La semaine sanglante (Paris, 1871)
4. 30,000 – 228 Incident, (Taiwan, 1947)
5. 11,000 – Romanian Peasants’ Revolt, 1907
6. 7,500 – March 1st Movement (Seoul, Korea, 1919)
7. 3,000 – Burma 1988 demonstrations (Yangon, (a.o.) Myanmar, 1988)
8. 1,000 – Bloody Sunday (1905) (St. Petersburg, Russia, 1905)
9. 500–2,600 – Aftermath of Tiananmen Square protests of 1989 (China, 1989)
10. 400 – Iranian pilgrim riot (Mecca, 1987) 

The most devastating natural disaster, excluding disease, in terms of death toll

Either 1931 Huang He flood (China, 1931) – 1,000,000–3,700,000 or 

Period of Three Difficult Years (famine) (China, 1958 – 1961) 1,000,000–43,000,000 -  (most estimates are between 20 and 30 million)

Contractible disease

1. 300,000,000+ – Smallpox (20th Century)
2. 200,000,000 – Bubonic Plague (worldwide, 1300s)
3. 100,000,000 – Plague of Justinian (Europe 540-590) (disputed)
4. 10,000,000 – 100,000,000 – deaths from diseases in Europe (millions) and the Americas (tens of millions) from diseases exchanged between continents after 1492
5. 20,000,000 – Spanish Flu (worldwide, 1918 – 1919)
6. 19,000,000 – AIDS (worldwide, 1981 – )
7. 10,000,000 – Bubonic Plague (China, 1892 – 1896)
8. 5,000,000 – Antonine Plague (Roman Empire 165 – 180)
9. 4,000,000 – Asian Flu pandemic (worldwide, 1957)
10. 1,000,000 – Hong Kong Flu pandemic (worldwide, 1968)
11. 130,000 – North American smallpox epidemic (1775 – 1782)
12. 60,000 – Great Plague of London (1665)
13. 775 – Severe Acute Respiratory Syndrome (SARS) (Mostly East Asia, few cases in Europe, Canada and United States, 2002-2003)
14. 677 – West Nile Virus outbreak (North America, 1999 – 2004)
15. 86 – H5N1 strain of bird flu (started in Asia) (late 2003-present)