The Columbia Encyclopedia, Sixth Edition.  2001
http://www.bartleby.com/65/we/Wends.html

Wends

or Sorbs, Slavic people (numbering over 100,000) of E Germany, in Lusatia. They speak Lusatian (also known as Sorbic or Wendish), a West Slavic language with two main dialects: Upper Lusatian, nearer to Czech, and Lower Lusatian, nearer to Polish. The towns of Bautzen (Upper Lusatia) and Cottbus (Lower Lusatia in modern Silesia) are their chief cultural centers. In the Middle Ages the term Wends was applied by the Germans to all the Slavs inhabiting the area between the Oder River in the east and the Elbe River and the Saale River in the west. German conquest of their land began in the 6th cent. and was completed under Charlemagne (8th cent.). A coalition of Wendish tribes in the 10th cent. and again in the early 12th cent. temporarily halted German expansion. A crusade against the pagan Wends was launched in 1147 under the leadership of Henry the Lion of Saxony and Albert the Bear of Brandenburg. The crusade itself was, on the whole, a failure, but in subsequent years Henry the Lion, aided by Waldemar I of Denmark, Albert the Bear, and other princes, carried out a systematic campaign of conquest. By the end of the 12th cent. nearly all Germany except East Prussia had been subjected to German rule and was Christianized. However, a group of Slavic-speaking Wends has maintained itself to the present day in Lusatia. They call themselves Srbi and hence are known also in English as Lusatian Sorbs or Serbs.

See G. Stone, The Smallest Slavonic Nation: The Sorbs of Lusatia (1972).