not sure why i looked this up, but it looks like stanford made a highscore list or something
nazis
88 should be #1 though. all deaths combined is like 39 mil, if i added right ;p
nazis

Code:
[B]A Record of Misery: mass killing in the past five decades[/B]
This table lists events involving 100,000 or more human deaths.
[B]Mass Killings[/B]
China: Mao's reign of terror, 1949-65 20 million plus [2,4,5]
USSR: Stalin's terror, 1936-53 20 million plus [1,2,5]
WWII: combatant deaths 16.8 million [4]
WWII: noncombatant deaths
Russia/USSR:civilian deaths by Nazis 7-12 million [4,5]
Europe: The Holocaust, 1933-45 6 million [1,4]
Other WWII noncombatant deaths 6 million [4]
Sino-Japanese War: 1937-45 3.5 million [4]
Korean War: 1950-53 2 million [4]
Eritrea: vs Cuba/Ethiopia, 1961-91,
inc. 1 mil. famine deaths 1984-85 2 million [4]
Vietnam War: 1961-75, incl. 600,000
noncombatants 1.7 million [4]
Cambodia: Khmer Rouge killing fields,
1975-79 1.6 million [4]
Afghanistan: vs. Soviets, 1979-89 1.3 million [4]
China: Civil war, 1945-49 1.2 million [4]
Rwanda: Hutus vs Tutsis, 3 months 1994 1 million [3]*
*Other estimates are of 500,000+ deaths
for this period (Economist 8/20/94 p.33)
Sudan: Civil war, 1955-72, 1983-
(incl. 250,000 famine deaths in 1988) 1 million [4]
Spain: Civil war, 1936-39 610,000 [4,7]
Nigeria: Civil war (Biafra), 1967-70,
including famine deaths 500,000 [4]
Kurdistan: Kurds vs Iraq, Iran, Syria,
Turkey, 1925- 500,000 [6]
India-Pakistan partition 1949 500,000
Iran-Iraq war, 1987-1992 500,000
Algeria: FLN vs France, 1954-62 300,000 [4]
Burundi: Tutsi slaughter of Hutus, 1972 300,000 [8]
Pakistan: Reprisals against Bengalis,
9 months in 1971 250,000 [4]
Indonesia: Civil war, 1965-66 250,000 [4]
Indonesia: Timor war, 1975-88 200,000 [4]
Bosnia: "Ethnic cleansing", 1992- 200,000 [3]
Congo: Congo-Kinshasa unrest, 1960-66 110,000 [7]
Rwanda: Hutu massacre of Tutsis, 1956-65 105,000 [7]
[B]Refugees[/B]
Afghanistan: 1979-94 6 million [3]
Rwanda: 3 months, 1994 2.4 million [3]
Mozambique: Civil war & famine, 1975-92 1.5 million [3]
Iraq: Kurds fleeing after Gulf War,
in 6 weeks, 1991 1.4 million [3]
Somalia: Civil war, 1988-94 1 million [3]