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After the assassination in Sarajevo, Austria issued an ultimatum with humiliating conditions to Serbia considering it responsible for the event. Serbia accepted all the conditions except the condition that “Austrian executives would have participated to the judicial inquiry against the assailants”. Austria considered insufficient that response and as consequence it declared war to Serbia on 28th July 1914.

From 25th to 30th July there were attempts to prevent that the war became a general war; but Russia, in order to support Serbia, ordered a general mobilisation threatening Austria and Germany. Faced with the threat Germany declared war to Russia on 31st July; France, allied with Russia, went to war on 2nd​ August; after a few days (4th​ August) also Great Britain went to war because its supremacy in the North Sea was threatened.

Even if Italy have been part of the Triple Alliance with Austria-Hungary and Germany since 1882, it declared its neutrality for the following reasons:
  • the alliance treaty was defensive and not offensive but in that occasion Austria caused the war.
  • that treaty declared that if Austria and Italy were forced to change their “status quo” in ​the East, they would have made agreements on mutual rewards but in that occasion Austria have declared war unbeknown to Italy.