Chaos and invasion made the taking of slaves habitual throughout Europe in the early Middle Ages. St. Patrick, himself captured and sold as a slave, protested an attack that enslaved newly baptized Christians in his Letter to the Soldiers of Coroticus.
Slavery during the Early Middle Ages had several distinct sources. The Vikings raided across Europe, though their slave raids were the most destructive in the British Isles and Eastern Europe. While the Vikings kept some slaves for themselves as servants, known as thralls, most people captured by the Vikings would be sold on the Byzantine or Islamic markets. In the West the targets of Viking slavery were primarily English, Irish, and Scottish, while in the East they were mainly Slavs. The Viking slave trade slowly ended in the 1000s, as the Vikings settled in the European territories they once raided, Christianized, and merged with the local populace.
The Islamic World was also a main factor in Medieval European slavery. From the early 700s until the early Modern time period (rough the 18th or 19th centuries) Muslims consistently took European slaves. This slavery began during the Muslim Conquest of Visigothic Spain and Portugal in the 8th century. The Muslim powers of Iberia both raided for slaves and purchased slaves from European merchants, often the Jewish Radhanites, one of the few groups that could easily move between the Christian and Islamic worlds. As the Muslims failed to conquer Europe in the 8th century they took to pirate raids against the shores of Spain, southern Portugal and France, and Italy, that would last roughly from the 9th century until the 12th century, when the Italian city-states of Genoa, Venice, and Pisa, along with the Spanish kingdoms of Aragon and Castile, as well as the Sicilian Normans, began to dominate the Mediterranean. The Middle Ages from 1100 to 1500 saw a continuation of the European slave trade, though with a shift from the Western Mediterranean Islamic nations to the Eastern, as Venice and Genoa, in firm control of the Eastern Mediterranean from the 12th century and the Black Sea from the 13th century sold both Slavic and Baltic slaves, as well as Georgians, Turks, and other ethnic groups of the Black Sea and Caucasus, to the Muslim nations of the Middle East. The sale of European slaves by Europeans slowly ended as the Slavic and Baltic ethnic groups Christianized by the Late Middle Ages. European slaves in the Islamic World would, however, continue into the Modern time period as Muslim pirates, primarily Algerians, with the support of the Ottoman Empire, raided European coasts and shipping from the 16th to the 19th centuries, ending their attacks with the naval decline of the Ottoman Empire in the late 16th and 17th centuries, as well as the European conquest of North Africa throughout the 19th century.
The Mongol invasions and conquests in the 13th century made the situation worse.[16] The Mongols enslaved skilled individuals, women and children and marched them to Karakorum or Sarai, whence they were sold throughout Eurasia. Many of these slaves were shipped to the slave market in Novgorod.[17][18][19]
Slave commerce during the Late Middle Ages was mainly in the hands of Venetian and Genoese merchants and cartels, who were involved in the slave trade with the Golden Horde. In 1382 the Golden Horde under Khan Tokhtamysh sacked Moscow, burning the city and carrying off thousands of inhabitants as slaves. Between 1414 and 1423, some 10,000 eastern European slaves were sold in Venice.[20] Genoese merchants organized the slave trade from the Crimea to Mamluk Egypt. For years the Khanates of Kazan and Astrakhan routinely made raids on Russian principalities for slaves and to plunder towns. Russian chronicles record about 40 raids of Kazan Khans on the Russian territories in the first half of the 16th century.[21] In 1521, the combined forces of Crimean Khan Mehmed Giray and his Kazan allies attacked Moscow and captured thousands of slaves.[22]
In 1441, Haci I Giray declared independence from the Golden Horde and established the Crimean Khanate. For a long time, until the early 18th century, the khanate maintained a massive slave trade with the Ottoman Empire and the Middle East. In a process called the "harvesting of the steppe", they enslaved many Slavic peasants. About 30 major Tatar raids were recorded into Muscovite territories between 1558-1596.[23] In 1571, the Crimean Tatars attacked and sacked Moscow, burning everything but the Kremlin and taking thousands of captives as slaves.[24] In Crimea, about 75% of the population consisted of slaves.[25]
Medieval Spain and Portugal were the scene of almost constant warfare between Muslims and Christians. Periodic raiding expeditions were sent from Al-Andalus to ravage the Iberian Christian kingdoms, bringing back booty and slaves. In a raid against Lisbon, Portugal in 1189, for example, the Almohad caliph Yaqub al-Mansur took 3,000 female and child captives, while his governor of Córdoba, in a subsequent attack upon Silves, Portugal in 1191, took 3,000 Christian slaves.[26]
The Byzantine-Ottoman wars and the Ottoman wars in Europe brought large numbers of Christian slaves into the Islamic world too.[27] After the battle of Lepanto approximately 12,000 Christian galley slaves were freed from the Ottoman Turks.[28] Christians were also selling Muslim slaves captured in war. The Knights of Malta attacked pirates and Muslim shipping, and their base became a centre for slave trading, selling captured North Africans and Turks. Malta remained a slave market until well into the late 18th century. It required a thousand slaves to equip merely the galleys (ships) of the Order.[29][30]
Slavery in Poland was forbidden in the 15th century; in Lithuania, slavery was formally abolished in 1588; they were replaced by the second enserfment. Slavery remained a minor institution in Russia until the 1723, when the Peter the Great converted the household slaves into house serfs. Russian agricultural slaves were formally converted into serfs earlier in 1679.[31] The runaway Polish and Russian serfs and kholops known as Cossacks (‘outlaws’) formed autonomous communities in the southern steppes.[32]