There would actually be no need to kill anybody in order to prevent WW1 and WW2 (at least as we know it) you'd simply need to tell a taxi driver to take a different path, and all would be well:
"But Franz was not yet done putting his life in insane danger. Against the advice of pretty much everyone, he insisted on going to the hospital to visit the people who were injured by the grenade. The driver, unfortunately, had no idea where the fuck he was going. They ended up crisscrossing hilariously through the streets of Sarajevo, until they just randomly happened to pass a cafe where, you guessed it, Gavrilo Princip was enjoying a post-failed-assassination sandwich.
After the obligatory pause of dumbfounded luck, Princip grabbed his pistol and turned the tide of history."
"But Franz was not yet done putting his life in insane danger. Against the advice of pretty much everyone, he insisted on going to the hospital to visit the people who were injured by the grenade. The driver, unfortunately, had no idea where the fuck he was going. They ended up crisscrossing hilariously through the streets of Sarajevo, until they just randomly happened to pass a cafe where, you guessed it, Gavrilo Princip was enjoying a post-failed-assassination sandwich.
After the obligatory pause of dumbfounded luck, Princip grabbed his pistol and turned the tide of history."
http://www.cracked.com/article_17298_6-random-coincidences-t...