Gavrilo Princip (1894-1918) may have been the most influential man of the
twentieth century, if we look at the total effect of what followed. His assassination of the
Archduke and his wife, Sophie sparked
World War I. The war inspired
Woodrow Wilson to involve the
United States in the conflict, paving the way for
American Imperialism and interventionist actions around the globe. The
Treaty of Versailles which followed punished
Germany, causing resentment, nationalism, and the rise of the
Nazis. This caused
World War II. The same treaty also carved up much of the
Middle East by weakening the
Ottoman Empire. This led to the destruction of the
Caliphate, paving the way for much of the strife in that region.
The war helped to bring about the end of the Czarist system in Russia, leading to the Soviet Union. World War II resulted in that union becoming a superpower, exporting communism across the globe. The early success communism had inspired Mao Zedong, and the methods they used were similar. The Vietnam War, Korean Conflict, and the Cold War all probably would never have happened if those shots had not been fired.
Indirectly, Gavrilo Princip may have caused the deaths of a couple of hundred million people. See the Law of Unintended Consequences. A good reason to look before you leap.
Princip was sentenced to 20 years in prison for his crime, since he was not 20 when he did it. He died in 1918 of tuberculosis. I wonder what he would have thought about what he did if he had lived to see the results.