The next day, Serbian reservists being transported on tramp steamers on the Danube crossed onto the Austro-Hungarian side of the river at Temes-Kubin and Austro-Hungarian soldiers fired into the air to warn them off. The report of this incident was initially sketchy and reported to Emperor Franz-Joseph erroneously as "a considerable skirmish". Austria-Hungary then declared war and mobilized the portion of its army that would face the (already mobilized) Serbian Army on 28 July 1914. Under the Secret Treaty of 1892 Russia and France were obliged to mobilize their armies if any of the Triple Alliance mobilized. Russia partially mobilized along its Austrian border on 29 July, and on 30 July Russia ordered general mobilization. Russia's general mobilization set off full Austro-Hungarian and German mobilizations. Soon all the Great Powers except Italy had chosen sides and gone to war.