In 1914, Russia entered World War I in response to Austria-Hungary's declaration of war on Russia's ally Serbia, and fought across multiple fronts while isolated from its Triple Entente allies. In 1916, the Brusilov Offensive of the Imperial Russian Army almost completely destroyed the Austro-Hungarian Army. However, the already-existing public distrust of the regime was deepened by the rising costs of war, high casualties, and rumors of corruption and treason. All this formed the climate for the Russian Revolution of 1917, carried out in two major acts.