The 28th of June 1914 Gavrilo Princip, a Serbian nationalist, killed the archduke Francis Ferdinand, who was heir to the throne in Austria, and his wife while they were visiting the city of Sarajevo. After a month Austria declared war to Serbia. Before the First World War, Europe was facing a very complicated situation due to political, economical and military problems.
Lots of nationalist tendencies were beginning to spread across the continent in early 1900. Furthermore there were secret societies in Serbia that wanted to abolish the Austria-Hungarian empire with a revolutionary act. The members of these societies were called “Young Bosnians”. They believed they could have stopped the Habsburg domination with a political murder. Already in 1910, Bogdan Zarajič, leader of the “Young Bosnians”, decided to kill the emperor Francesco Giuseppe in Monstar, but he changed his mind at last. Some days later he shot the governor of Bosnia.
So when the “Young Bosnians” discovered that the archduke Francis Ferdinand was going to visit Sarajevo, they thought that killing him would have been a great way to reach their goal.
When Francis Ferdinand went to witness the military manoeuvres in Bosnia, a first guy threw a grenade at their car. The attempt wasn’t successful as only some of the soldiers were wounded. But while the archduke was headed to see his soldiers in the hospital, Gavrilo Princip seized the moment and shot both the archduke and his wife killing them instantaneously. The killer was immediately arrested by the guards.
In a different political situation in Europe, this act would have only lead to a war in the Balkans or in Central Europe.
Unfortunately within days the conflict became of much bigger dimensions when the tsar of Russia, who was allied with France and Great Britain (Triple Entente), prepared the troops to send for the war. On the other hand, Germany, counting on the power of its Alliance with Italy and Austria (the Triple Alliance), responded by preparing its own troops. The tension created served as the trigger for the biggest war that the World had ever seen.
In Albert Mousset’s book L’attentat de Sarajevo : un drame historique : documents inedits et texte integral des stenogrammes du proces, Paris, Payot, 1930 is written that Gavrilo Princip during the trial said:  “I’m not a criminal, because I killed an evil man. I’m a nationalist from Yugoslavia. I want to unite all the Yugoslavians and free them from the Austrian domination which is bad for our country.”

In the past there had already been other attempted murders to the authorities in different countries. For example the one involving the king Umberto I who was shot in July 1900 by the anarchic Gaetano Bresci.

In general revolutionaries use assassinations to oppose the power, but only in a few cases they succeed in their purpose.