10 Worst Ways History Has Repeated Itself

Rwandese refugees cross the border into Tanzania in 1994. REUTERS/Jeremiah Kamau/Files/Corbis

When people think of genocide, chances are their minds quickly turn to the Holocaust. During the horrific event, Nazi Germany systematically rounded up and imprisoned Jewish, gays, Roma people, communists and others who did not fit into Hitler's worldview. There, some 11 million concentration camp prisoners ultimately died from starvation, exhaustion or execution. It was so terrible, in fact, that German schools now mandate teaching of the Holocaust in hopes that future generations will never repeat the mistakes of their past [source: Frontline]. And other countries have pledged to stop it if it does happen. "[N]ever again will the world ... fail to act in time to prevent this terrible crime of genocide," U.S. President Jimmy Carter proclaimed in 1979 [source: Holocaust Museum, FAQs].

But did you know there have been as many as two dozen instances of genocide since the Holocaust? [source: Inter-Parliamentary Alliance] That figure depends on how genocide is defined, but generally it involves violent crimes carried out against a group of people with the ultimate intent to exterminate them. Take Cambodia's Khmer Rouge, which, between 1975 and 1979, killed as many as 2 million political dissidents — a shocking one-third of the country's population. Just 15 years later, during a 100-day span in 1994, Rwanda's Hutu government killed between one-half and 1 million Tutsis. Such crimes continue in the 2010s, as some leaders have accused Syrian president Bashar al-Assad of killing his own people to retain power [source: Holocaust Museum, Cases].