The Russian Empire (Pre-reform Russian orthography: Россійская Имперія, Modern Russian: Российская империя, translit: Rossiyskaya Imperiya) was a state that existed from 1721 until overthrown by the short-lived liberal February Revolution in 1917. One of the largest empires in world history, stretching over three continents, the Russian Empire was surpassed in landmass only by the British and Mongol empires. It played a major role in 1812-14 in defeating Napoleon's ambitions to control Europe, and expanded to the west and south. It was often in conflict with the Ottoman Empire (which in turn was usually protected by the British).
At the beginning of the 19th century, the Russian Empire extended from the Arctic Ocean in the north to the Black Sea on the south, from the Baltic Sea on the west to the Pacific Ocean, and (until 1867) into Alaska in North America on the east. With 125.6 million subjects registered by the 1897 census, it had the third largest population in the world at the time, after Qing China and the British Empire. Like all empires, it included a large disparity in terms of economics, ethnicity, and religion. There were numerous dissident elements, who launched numerous rebellions and assassination attempts; they were closely watched by the secret police, with thousands exiled to Siberia.
Economically, the empire was heavily rural, with low productivity on large estates worked by serfs, until they were freed in 1861. The economy slowly industrialized with the help of foreign investments in railways and factories. The land was ruled by a nobility called Boyars from the 10th through the 17th centuries, and then was ruled by an emperor called the "Tsar". Tsar Ivan III (1462–1505) laid the groundwork for the empire that later emerged. He tripled the territory of his state, ended the dominance of the Golden Horde, renovated the Moscow Kremlin, and laid the foundations of the Russian state. Tsar Peter the Great (1682–1725) fought numerous wars and built a huge empire that became a major European power. He moved the capital from Moscow to the new model city of St. Petersburg, and led a cultural revolution that replaced some of the traditionalist and medieval social and political system with a modern, scientific, Europe-oriented, and rationalist system.
Catherine the Great (1761–1796) presided over a golden age. She expanded the nation rapidly by conquest, colonization and diplomacy. She continued Peter the Great's policy of modernisation along West European lines. Tsar Alexander II (1855–1881) promoted numerous reforms, most dramatically the emancipation of all 23 million serfs in 1861. His policy in Eastern Europe was to protect the Orthodox Christians under the rule of the Ottoman Empire. That involvement by 1914 led to Russia's entry into the First World War on the side of France, Britain, and Serbia, against the German, Austrian and Ottoman empires. Russia was an absolute monarchy until the Revolution of 1905 and then became a constitutional monarchy. The empire collapsed during the February Revolution of 1917, largely the result of massive failures in its participation in the First World War.