Complex sentence: The Liutizian lands were incorporated in the Holy Roman Empire until 1164 and, after a period of Danish raids and occupation, settled by Germans in the Ostsiedlung thereafter, the remnants of the Slavic tribes were gradually Germanized and assimilated during the following centuries.
Split into simpler sentences: The Liutizian lands were subject to the Holy Roman Empire until 1164 and, after a period of Danish raids and occupation, settled by Germans in the Ostsiedlung thereafter. The remnants of the Slavic tribes were gradually Germanized and assimilated during the following centuries.