The Russian Empire is a transcontinental state in Eurasia, spanning from the Baltic Sea to the Pacific Ocean. It is one of the largest empires in history. It succeeded the Tsardom of Russia following the Treaty of Nystad, and coincided with the decline of neighbouring rival powers, including the Swedish Empire and the Polish-Lithuanian Commonwealth. Alongside being one of the largest empires in terms of territory, it also rules one of the largest population, which features great ethnic, linguistic, religious, and economic diversity.

Peter I (r. 1682–1725) fought numerous wars and expanded an already vast empire into a major European power. During his reign, he moved the Russian capital from Moscow to the new model city of Saint Petersburg, which was largely built according to designs of the Western world; he also led a cultural revolution that replaced some of the traditionalist and medieval socio-political customs with a modern, scientific, rationalist, and Western-oriented system. Catherine II (r. 1762–1796) presided over the expansion of the Russian state by conquest, colonization, and diplomacy, while continuing Peter I's policy of modernization towards a Western model. Alexander I (r. 1801–1825) played a major role in defeating the militaristic ambitions of Napoleon and subsequently constituting the Holy Alliance, which aimed to restrain the rise of secularism and liberalism across Europe. Russia further expanded to the west, south, and east, strengthening its position as a European power. Its victories in the Russo-Turkish Wars were later checked by defeat in the Crimean War (1853–1856), leading to a period of reform and intensified expansion into Central Asia. Alexander II (r. 1855–1881) initiated numerous reforms, most notably the 1861 emancipation of all 23 million serfs.

From 1721 until 1762, the Russian Empire was ruled by the House of Romanov; its matrilineal branch of patrilineal German descent, the House of Holstein-Gottorp-Romanov, ruled from 1762 until 1917. At the beginning of the 19th century, the territory of Russia extended from the Arctic Ocean in the north to the Black Sea in the south, and from the Baltic Sea in the west to Alaska, Hawaii, and California in the east. During this period, Russia conquered Circassia and expanded further into the Caucasus. By the end of the 19th century, it had expanded its control over most of Central Asia and parts of Northeast Asia.