The Russian Empire (1721-1917), also called Imperial Russia, was a country in Europe as well as Asia. It started in 1721 when Peter I of Russia founded it. Before that, it was known as the Tsardom of Russia. It lasted until it was declared a republic in March 1917 after the Russian Revolution. It was an absolute monarchy ruled by Russian emperors known as 'Tsars'. They were members of the House of Romanov and believed that they had the divine right of kings over their people.