How World War I started

The Balkans were a smoldering powder keg ready to explode. The spark was
supplied in the form of the assassination of Archduke Ferdinand while he
was visiting Sarajevo (June 28, 1914). Then...

Germany urged Austria-Hungary to retaliate against the Serbia.
Austria-Hungary declared war on Serbia (July 28, 1914)

Russia came to Serbia's aid.

Germany declared war on Russia.

France pledged support to Russia.

Germany declared war on France.

To access Paris, Germany invaded Belgium. This brought England into the
War. England declares war on Germany (August 4, 1914)

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Armistice day celebrates the official end of WWI (11th hour on the 11th
day of the 11th month 1918).

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Contributing factors:
* Fervent and uncompromising nationalism
* Unresolved previous disputes
* The intricate system of alliances
* Convoluted and fragmented governance
* Delays and misunderstandings in diplomatic communications
* The arms races of the previous decades.
* Rigidity in military planning