Russia is a relatively new nation much like Germany (formerly Prussia). They grew into a nation under the Tsars. The Revolution was the Whites (royal family) vs the Reds (communists Bolshevik and Menshevik). Tsar Nicholas II was inept and cruel as a leader and due to his failure to even keep the Russo - Japanese War close AND getting pulled into The Great War with a starving nation he got a revolution and lost.

Yes the Russians were allied with the Serbs in The Great War so when Austria-Hungary declared war on Serbia the Russians were in. France is deeply allied with Russia at this time and England sides with them because mutual enemy Germany wanted the greatest navy. The United States remained out for a while and oddly enough there had almost been a build up to war with England and Canada (how silly!).