Schleswig-Holstein Historical Geography

In the second half of the 7th century the Slavs arrived in East Holstein. They were the Wagrier and the Polaben, who pushed forward to the Kiel Fjord and down to the river Elbe. They built castles (the first one in Oldenburg) and settled around them. http://de.wikipedia.org/wiki/Wagrien

During the first half of the 8th century, the Jüten (Danish tribe) started to settle areas around the river Schlei (Haithabu). The Jüten continued to spread over the next centuries. http://en.wikipedia.org/wiki/Hedeby

North Friesland was settled by Frisians from Friesland starting in the 8th century with Eiderstedt. In the 11th century they made the marshes accessible. http://en.wikipedia.org/wiki/Frisians

In Holstein the three Saxon tribes Holsten, Dithmarscher and Stormaren established their settlements.

All these different races were separated from each other by either natural borders, such as rivers, fjords or landscapes or by manmade borders, such as the Danewerk which was protect against the Germans. http://encyclopedia.jrank.org/DAH_DEM/DANNEWERK_or_DANEWERK_Danish_Da.html