Answer:
The Czar of Russia, Nicholas II, starts calling up for a full mobilization of his army on July 29th, 1914, as a response to Germany´s ambiguous stance on whether they would react militarily to a Russian intervention against Austria if they attacked Serbia, or if they would stay neutral, as the Kaiser had told the Czar they would. These ambiguous messages, one from the German military, and the other from the Kaiser, forced Russia to take action and prepare itself in case of a German attack against them. It was this lack of clear decision, this dangerous game from Wilhelm II, Kaiser of Germany, which led to a further destabilization of peace in Europe; the original destabilizer having been the murder of Archduke Franz Ferdinand on June 28th, 1914, in Bosnia, which led to a war declaration from the Austrio-Hugarian Empire against Serbia.