Imperial Coat of Arms of the Austrian Empire
On June 28th. 1914, Archduke Franz Ferdinand of Austria and his wife,
Sophie, Duchess of Hohenberg were killed in Sarajevo
(then located in Austria - Hungary).
Archduke Franz Ferdinand and his family - Source picture: Wikipedia
When the Austrians heard the news of the assassinations they were very angry.
They thought that Serbia was involved in the murder.
The site of the assassination - Source picture: Wikipedia
On July 28th. 1914, Austria (supported by Germany) declared war to Serbia.
This marks the start of World War I.