The Archduke Franz Ferdinand of Austria was assassinated on June 28 1914. This event was the key turning points in twentieth century history. The Archduke, heir presumptive to the Austro-Hungarian throne, was shot in Sarajevo by Gavrilo Princip. The assassin was a member of the Black Hand gang, a Serbian nationalists group, whose aim was to free Serbia of the rule of the Austro-Hungarian empire.
The killing caused Austria-Hungary to declare war on Serbia. This in turn precipitated a political crisis between the Great Powers in Europe which led to a chain of events which brought about the outbreak of the First World War.
We don't realise the enormity or impart of this event. The murder of Archduke Franz Ferdinand of Austria in Sarajevo in 1914 would be like the the assassination of the Prince of Wales in the streets of Dublin. George Bernard Shaw, in his discarded defence of Roger Casement, wrote:
"On the question of allegiance, Roger Casement was equally explicit. He pointed out that five centuries of Turkish rule in the Balkans had not, in the opinion of the British nation, abrogated the right of every Serbian to strike for independence, and he co concluded quite logically that the same period of British rule could not abrogate the right of every Irishman to do the same. In England we are still so strongly of the opinion so far as Serbia is concerned that we have not allowed an event which could be paralleled in these islands but by the assassination of the Prince of Wales in the streets of Dublin to shake our adherence to, and our support by armed force of, this principle of nationality. It seems to me that Casement is here quite unanswerable."
It's an indulgence, but if we engage in "what if-ery" and counter-factual thought experiment, without the assassination of Franz Ferdinand Hitler may well have pursued his interest in alternative medicine, Lenin may have become a professor of Russian politics at Columbia University.