Between the 6th and 10th centuries AD, the primary source of slaves for Europe and the Middle East were the territories of Central and Eastern Europe, especially Slavonic people. This is why the word for slave in many European languages is derived from the word for Slavs (in English, German and French, for example). Another important source for the Middle East was West Africa, via the trans-Saharan trade routes.

After the conquest of North Africa and Spain by Muslims, the Islamic World became a huge importer of slaves from Central Europe. The trade routes were established between slave trade centres in the Slavonic countries (for example Prague and Wolin) and Arab metropoles in Spain. Because of religious constraints, the slave trade was monopolised by Jews who were able to transfer the slaves from Pagan Central Europe through Christian Western Europe to Muslim countries in Spain and Africa. The majority of slaves were prisoners captured in wars between Slavonic tribes and states.

This trade came to the end in 10th century after the Christianisation of the Central European Slavic countries.

Serfdom replaced the institutition of slavery. While serfdom had numerous disadvantages, it was in no way equivalent with slavery. For example, the serf had numerous rights the slave had not: could marry, have a family, pass on his family inheritance, and cultivate the land.

Further reading: those terrible middle ages, by Regine Pernoud

Saint Adalbert was one person that wanted to put an end to the slave trade.