The Rwandan genocide started when the president of that country, Juvénal Habyarimana, was assassinated. His plane was shot down above Kigali International Airport on April 6 1994. Habyarimana was a Hutu. Soon after the assassination, nearly 1 million Tutsis were killed in revenge.
World War 1 started after the assassination of Archduke Franz Ferdinand of Austria by Bosnian Serb teenager Gavrilo Princip. It is estimated that close to 40 million people were killed during that war.