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 (Limes Saxoniea) or by manmade borders, such as the Danewerk which was to protect against the Germans. http://encyclopedia.jrank.org/DAH_DEM/DANNEWERK_or_DANEWERK_Danish_Da.html

In the early 8th century Holstein became part of Charlemagne's empire. The Danes reigned north of the Eider, the Franken south of the river. The close connection of the Holsten, Dithmarscher and Stormaren with the Franken was replaced in the 10th century by Saxon margraves and dukes. With new leadership colonists from all over Germany and the Netherlands were invited to settle in Holstein. The Holsten themselves had first pickings and moved eastwards to push aside the Slavs inasmuch as they did not want to comply with agricultural methods the Holsteiners brought with them. The Slavs were compelled to intergrate.

Source:

Historischer Atlas Schleswig-Holstein. Vom Mittelalter bis 1867. Wachholtz Verlag, Neumünster 2004