Imperial Russia refers to the period of Russian history from 1721, when Peter the Great declared the Russian Empire, until the abdication of Tsar Nicholas II in 1917. This era was marked by significant territorial expansion, cultural development, and the establishment of a centralized autocratic government. The empire became one of the largest in history, stretching across Europe and Asia. During this time, notable figures such as Catherine the Great and Alexander II played crucial roles in modernizing the country and implementing reforms. The empire faced various challenges, including social unrest, economic difficulties, and military conflicts, ultimately leading to the Russian Revolution and the end of imperial rule.