Answer:
On June 24, 1914 Franz Ferdinand, archduke of Austria-Hungary, was visiting the city of Sarajevo (province of Bosnia Herzegovina). For many people, the visit was considered a provocation. For example, for young Serbian nationalists who wanted Serbia to recover the province of Bosnia-Herzegovina.
Several went out to protest and one of the young men threw a grenade at the vehicle in which Franz Ferdinand and his wife were going. When the grenade exploded several people were injured. The imperial couple had no injuries but they canceled their tour. Instead, they decided to go to the hospital to visit an officer who had been injured, and during the trip they were killed.
This murder unleashed a series of protests and a month later, on July 28, Austria-Hungary declared war on Serbia. Chaos grew like a snowball. Russia got involved as it had alliances with Serbia. Germany, an ally of Austria-Hungary, declared war on Russia. The United Kingdom declared war on Germany, after the Germans invaded Belgium.
This story led to the First World War that changed the direction of Europe.
