The Tsar to Stalin period represents some of the most turbulent times in the history of Russia.
The last Tsar of Russia was Nicholas II, whose regime collapsed in 1917, during the World War I. The communists were gaining power for some time and capitalized on the suffering faced by the people. The tsar's regime was marked by a number of wars, including those with Japan and World War I. Communists, under the leadership of Lenin, overthrew this oppressive regime and formed the Russian Republic (Russian Socialist Federative Soviet Republic). Communist policies were immediately implemented, including free healthcare and education, legalized homosexuality and abortions, nationalized estates and land, etc. A regime of terror and civil war followed, where the members of the former ruling class and aristocrats fought against the communists and lost. These anti-revolutionists were executed in the Red Terror and absolute Bolshevik control was established. The process of industrialization was started to lead the country on the path of progress. Russia SFSR became the Soviet Republic in 1922 after integrating former territories of the Russian Empire; with Lenin as its head. After Lenin's death, Stalin came to power and remained the Premier of the USSR until his death in 1953. Stalin initiated industrialization and consolidated his stature as the sole authority. All those who opposed him were killed (or purged) and thus millions were executed. Stalin was also the leader of the USSR through World War II and led his country to victory over Germany. He also brought his country into the Nuclear age and made it one of the superpowers of the world.
Thus, from the tsar to Stalin, the nation changed from monarchy to communism, from agrarian society to an industrial one, from a powerful country to a superpower; yet the absolute authority of one person was maintained.