World War I started when Austria-Hungary attempted (justly by most accounts) to punish Serbia for an assassination. Russia, foolishly and needlessly, elected to support the Serbs and declare war on A-H. Germany then was obligated to declare war on Russia; and France, in turn - and with England in tow, to declare war on Germany.
Ultimately, Russia suffered the 70-year-blight of Communism plus land losses in at the treaty of Brest-Litovsk: 1/3 of Poland, the Baltic states, parts of Czechoslavakia (Russia "surrendered" to Germany before the Germans did so to the Allies).