The lead up to World War One
Franz Ferdinand was an Archduke of Austria-Este, Austro-Hungarian and Royal Prince of Hungary and of Bohemia, and from 1889 until his death, heir presumptive to the Austro-Hungarian throne. He was assassinated at Sarajevo on 28 June 1914 by Gavrilo Princip, a Yugoslav nationalist.
The assassination precipitated Austria-Hungary’s declaration of war against Serbia on 28 July 1914. This caused the Central Powers including Germany and Austria-Hungary and the countries allied with Serbia (Russia and France) to declare war on each other, starting World War I.
When war broke out in August 1914, Germany, Austria-Hungary, Russia and France were all bound by their commitments to their allies. They had to go to war. Britain was not in that position, but despite this, Britain decided to join in the war on the side of Russia and France.
The Great War lasted from 1914-18. It was the most destructive war that had ever been fought. The total number of military and civilian casualties in World War I was over 37 million. There were over 16 million deaths and 20 million wounded ranking it among the deadliest conflicts in human history. The total number of deaths includes about 10 million military personnel and about 7 million civilians.
Source: Wikipedia and National Archives Image of Franz Ferdinand from Wikicommons