On June 28th in 1914, Archduke Franz Ferdinand was shot dead with his wife in Sarajevo. This image shows the pair about to enter the car in which they were both to be killed by Gavrilo Princip.

Archduke Franz Ferdinand Assassination

This event, helped along by a certain amount of chance, is seen as being the moment which started the First World War, changing the face of the world. 

For a more detailed understanding of how the war unfolded, Matthias Strohn's book 'World War I Companion' is a good starting point.

You can see the original image here.