In a secret agreement signed on 26 April in London, Italy agreed to leave the Triple Alliance, join the forces of the Triple Entente, and declare war on Austria-Hungary and Germany.

On the 23rd July 1914, Austria-Hungary issued an ultimatum to Serbia specifically designed to be rejected and lead to war between the two countries.

The National Assembly of Romanians of Transylvania and Hungary declared the unification of Transylvania and the Kingdom of Romania.

Keen to consolidate the newly-united Germany, Chancellor Otto von Bismarck turned to diplomacy in an attempt to ensure the status quo in Europe.

Germany and Russia signed the secret Reinsurance Treaty that ensured they would each remain neutral if the other went to war with a third European power.