Russia's role in the war was mostly that of fanning the flames. When Serbs in Serbia wanted to reunite with the Serbs in Bosnia-Herzegovina, Russia encouraged the Serbs in Bosnia-Herzegovina to rise up against the Austro-Hungarian government under their leadership. They did this because they wanted land in the Balkans. Russia also had the largest military is Europe, so when Austria-Hungary declared war on Serbia, Russia felt they had to prove themselves as allies of the Serbs. So, when war was declared, Russia started to mobilize its troops. This reaction to the declaration of war added to Europe's aggression, and is why I think Russia was a player in the start of the war.
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