Russian Empire (1721-1917)
In world war one, the empire entered when Austria-Hungary declared war on Serbia a Russian-protected country. When they entered the war, The German empire would shortly declare war on Russia due to declaring war on A-H, and France would enter not long after.
The Germans made heavy advances into Poland, Ukraine, Latvia, Lithuania, Estonia, Belarus, and western Euro-Russia. Shortly after this, Bolsheviks would rise up, and other communist parties in Russia. These uprisings would be caused due to the people upset over the tsardom, and the low levels of freedom and care for the lower class. Things like shortage of food, decrease of nationalism after the Germans made heavy advances in the west.
The Tsar would then short after abdicate, asking a possible heir member to take place, however they declined, which marked the end of the Russian monarchy. This would then create the more democratic provisional government, who took place after the monarchy. The provisional government would still continue to fight against the Central Powers, meanwhile, Germany would send Lenin, who was in Switzerland, to Russia to start a civil war.
After that, the peasants, with the help of Lenin, would revolt against the empire, and in 1917, the civil war would start, and the Russians would be forced to leave the world war when Germany signs a pact with the White Russians, who were the provisionial government. After this, the civil war would start, and the White Army, the provisionial government, would fight against the Red army, the communists. Shortly after, the Red army would win, and would create the Russian Soviet Republic once they won, which would shortly soon become into the USSR, or the United Soviet Socalist republics, encompassing mostly the same borders of the Russian empire, minus Poland, Baltics, and Finland.