The Russian Empire was an empire that spanned most of northern Eurasia from its establishment in November 1721 until the proclamation of the Russian Republic in September 1917. At its height in the late 19th century, it covered about 22,800,000 km (8,800,000 sq mi), roughly one-sixth of the world's landmass, making it the third-largest empire in history, behind only the British and Mongol empires. It also colonized Alaska between 1799 and 1867. The empire's 1897 census, the only one it conducted, found a population of 125.6 million with considerable ethnic, linguistic, religious, and socioeconomic diversity.
From the 10th to 17th century, the Russians had been ruled by a noble class known as the boyars, above whom was the tsar, the absolute monarch. The groundwork of the Russian Empire was laid by Ivan III who ruled from 1462 to 1505, and greatly expanded his domain, established a centralized Russian national state, and secured independence against the Tatars. His grandson, Ivan IV (r. 1533–1584), became in 1547 the first Russian monarch to be crowned tsar of all Russia. Between 1550 and 1700, the Russian state grew by an average of 35,000 km (14,000 sq mi) per year. Peter I transformed the tsardom into an empire, and fought numerous wars that turned a vast realm into a major European power. He moved the Russian capital from Moscow to the new model city of Saint Petersburg, and led a cultural revolution that introduced a modern, scientific, rationalist, and Western-oriented system. Catherine the Great (r. 1762–1796) presided over further expansion of the Russian state by conquest, colonization, and diplomacy, while continuing Peter's policy of modernization. Alexander I (r. 1801–1825) helped defeat the militaristic ambitions of Napoleon and subsequently constituted 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 conquests in Central Asia. Alexander II (r. 1855–1881) initiated numerous reforms, most notably the 1861 emancipation of all 23 million serfs.
