The Russian Empire, also known as Imperial Russia,[e][f] was the final period of the Russian monarchy from its proclamation in November 1721, until its dissolution in late 1917. It consisted of most of northern Eurasia. The Empire succeeded the Tsardom of Russia following the Treaty of Nystad. The rise of the Russian Empire coincided with the decline of neighbouring rival powers: the Swedish Empire, the Polish–Lithuanian Commonwealth, Qajar Iran, the Ottoman Empire, and Qing China. It also held colonies in Russian America between 1799 and 1867. Covering an area of approximately 22,800,000 square kilometres (8,800,000 sq mi), it remains the third-largest empire in history, surpassed only by the British Empire and the Mongol Empire; it ruled over a population of 125.6 million people per the 1897 Russian census, the only census carried out during the entire imperial period. Owing to its geographic extent across Europe, Asia, and North America at its peak, it featured great ethnic, linguistic, religious, and economic diversity.

From the 10th to the 17th century, the land was ruled by a noble class known as the boyars, above whom was a tsar (later adapted as the "Emperor of all the Russias"). The groundwork leading up to the establishment of the Russian Empire was laid by Ivan III (1462–1505): he tripled the territory of the Russian state and laid its foundation, renovating the Moscow Kremlin and also ending the dominance of the Golden Horde.

Peter I (1682–1725) fought numerous wars and expanded an already vast empire into a major power of Europe. During his rule, 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 the Great (1762–1796) presided over a golden age: she expanded the Russian state by conquest, colonization, and diplomacy, while continuing Peter I's policy of modernization towards a Western model. Alexander I (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. The Russian Empire 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.[8] Alexander II (1855–1881) initiated numerous reforms, most notably the 1861 emancipation of all 23 million serfs. His official policy involved the responsibility of the Russian Empire towards the protection of Eastern Orthodox Christians residing within the Ottoman-ruled territories of Europe; this was one of the factors that later led to the Russian entry into World War I.

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 the Russian Empire 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. By the end of the 19th century, it had expanded its control over most of Central Asia and parts of Northeast Asia. The Russian Empire entered the twentieth century in a perilous state. A devastating famine in 1891–92, killed millions across the empire leading to discontent among the population. Moreover, the Russian Empire was the last remaining absolute monarchy in Europe, which played a role in the rapid radicalization of Russian politics. During this time, communism became popular among much of the population.[9] In 1905 Russia experienced a revolution in which Tsar Nicholas II authorized the creation of a parliament, the State Duma, although he still retained absolute political power. When Russia entered the First World War on the side of the Allies, it suffered a series of defeats that further galvanized the population against the empire and the Tsar. In 1917, mass unrest among the population and mutinies in the army resulted in Russian leaders pressuring Tsar Nicholas to abdicate, which he did during the February Revolution. Following his abdication, the Russian Provisional Government was formed and continued Russia's involvement in the war, despite near universal opposition to further involvement. This decision, coupled with food shortages, led to mass demonstrations against the government in July. The Russian Provisional government was overthrown in the October Revolution by the Bolsheviks, who ended Russia's involvement in WWI with the Treaty of Brest-Litovsk. Russia was one of the of the four continental empires which collapsed after World War I, along with Germany, Austria-Hungary, and the Ottoman Empire (in 1922).[10]

The Bolshevik seizure of power resulted in the Russian Civil War, which pitted the Bolsheviks (Reds) against their adversaries (Whites).[11][12] The White Army was not a unified front and comprised many of the Bolsheviks' enemies on both the left and right. In 1918, the Bolsheviks executed the Romanov family, ending three centuries of Romanov rule. After emerging victorious from the Russian Civil War in 1922–1923, the Bolsheviks established the Soviet Union across most of the territory of the former Russian Empire.