Romania was important because it helped the Allies cut off the ties between Germany and Austria-Hungary with Ottomans and Bulgaria. This made it possible for Allies to fight the former without worrying that Ottomans will rush in to help. The impact of the Russian revolution was that the Russians withdrew from the war and this made life hard for people in the eastern fronts because it gave large parts of land to Germans and Ottomans. It was also bad for militaries like the Romanian and Serbian military who relied on Russian help in the east since the western forces were far away.
