the Herero and Nama peoples of Southwest Africa | 1904–1907 | in current-day Namibia | 75000 | ethnic/territorial |
Tutsis and moderate Hutus, | April 1994 | Rwanda | 937,000 | ethnic |
Sudan | 1983 - present | Sudan | 2000000 | ethnic |
Kurdish populations | 1986-88 | Iraq | 182,000 | religious/ethnic |
Assyrians | 1914–1923 | Turkey | 500,000 to 750,000 | religious/ethnic |
Armenians | 1915-1917 | Turkey | 600,000 to 1.5 million | religious/ethnic |
Pontian Greeks | 1914–1923 | Turkey | 300,000 to 600,000 | religious/ethnic |
Bosnian Muslims | 1992–1995 | Bosnia | 8,000 | religious/ethnic |
Serbs, Jews and Gypsies | 1941 - 1945 | Croatia | 80,000 to 100,000 | religious |
Jews, Roma, Slavs, homosexuals, communists | 1933–1945 | Germany | 11 million | territorial/ethnic/religious |
Ukrainians | 1932–1933 | USSR | 6,000,000 to 10,000,000 | communism |
Cambodians ethnic Vietnamese, ethnic Chinese or Sino-Khmers, ethnic Chams, ethnic Thais, Buddhist monks, secular intellectuals | 1975–1979 | Cambodia | 1.7 million | ethnic/communism |
tibetians | 1950s and 1960s | Tibet | 400,000 | communism |
Degar | 1973 - Present | Vietnam | 2 to 2.5 million | ethinc/communism |
Hindus | 1947 | India (partition) | 5 million | religious |
Sikh | 1919 | Amritsar (India) | 400 | religious/territorial |
Hindus | 1989 - present | Kashmir | 45,000+ | religous/territorial |
Bangladeshis | 1971 | Bangladesh | 3 million | territorial |
chinese | 1959 - 1961 | China | 15 to 30 million | political/communism |
totals communism | 25,100,000 |
ethnic | 19,302,000 |
religion | 17,715,400 |
territorial | 14,120,400 |
I have placed the Holocaust as having a religious element not becuase it was aimed at the Jews but because Nazism was not an atheist society. There was a state religion deliberately built around the Aryan race, going so far as to generate it's own rituals for marrage.
I have not put the deaths of the Great Leap Forward under a religious category as at that time the personality cult that Mao Tse-Tung formed around himself had not yet fully formed. During the Cultural Revolution this personality cult can hardly be classified as anything other than a, short lived, state religion. However I have no figures for the deaths during that time so I could not include it.
Communism was the most deadly ideology of the 20 century in terms of genocide. After that is ethnic strife. Third is religion with a mere 17 million (mainly due to the state religion of the Nazis) despite this often being called a secular century. Finally comes territorial expantion, and a desire to wipe out any inhabitants in order to gain the maximum new space and start with a clean slate.
It should be noted that the number killed by basically liberal secular states is 400 at Amritsar, which pales in comparison to what happens when you unlease totalitarianism or religion on a people. The numbers may show religion and communism in a better light if the 19th century are included as there where many more deaths from secular liberal states during this time as they carved out their empires and the communist states where not formed until the early 20th century.
If you look at the number of times a particular cause is implicated teh number one is ethinic strife. Number two is religion, with territorial expanision and communism in third and forth place. So communism may not have caused many but the ones it did where big. Religion may have been at the root on lots of massacares, but they tended to be of more limited scope.
Data from Wikipedia