The term serf, in the sense of an unfree peasant of tsarist Russia, is the usual English-language translation of () which meant an unfree person who, unlike a slave, historically could be sold only with the land to which they were "attached". Peter I ended slavery in Russia in 1723. Contemporary legal documents, such as Russkaya Pravda (12th century onwards), distinguished several degrees of feudal dependency of peasants. Serfdom became the dominant form of relation between Russian peasants and nobility in the 17th century. Serfdom most commonly existed in the central and southern areas of the Tsardom of Russia and, from 1721, of the subsequent Russian Empire. Serfdom in Little Russia (parts of today central Ukraine), and other Cossack lands, in the Urals and in Siberia generally occurred rarely until, during the reign of Catherine the Great (r. 1762–1796), it spread to Ukraine; noblemen began to send their serfs into Cossack lands in an attempt to harvest their extensive untapped natural resources. Only the Russian state and Russian noblemen had the legal right to own serfs, but in practice commercial firms sold Russian serfs as slaves – not only within Russia but even abroad (especially into Persia and the Ottoman Empire) as "students or servants". Those "students and servants" were in fact owned by rich people, sometimes even by rich serfs, who were not noblemen. Emperor Nicholas I banned the trade in African slaves in 1842, though there were almost no Russians who participated in it, but Russian serfs were still sold and bought. Emperor Alexander I () wanted to reform the system but moved cautiously, liberating serfs in Estonia (1816), Livonia (1816), and Courland (1817) only. New laws allowed all classes (except the serfs) to own land, a privilege previously confined to the nobility. Emperor Alexander II abolished serfdom in the emancipation reform of 1861, a few years later than Austria and other German states. Scholars have proposed multiple overlapping reasons to account for the abolition, including fear of a large-scale revolt by the serfs, the government's financial needs, changing cultural sensibilities, and the military's need for soldiers. Terminology The term , or () means "Russian peasant" when it is used in English. This word was borrowed from Russian into Western languages through translations of 19th-century Russian literature, describing Russian rural life of those times, and where the word muzhik was used to mean the most common rural dweller