The Rhenish Duchy of Berg and the Westphalian County of Mark in the west remained an obstacle to a land connection with the Cologne territory on the Lower Rhine river.

Apart from the fertile Hellweg Börde north of the Haar hill range, part of the Westphalian Lowland, the ducal lands primarily comprised mountainous and densely forested areas, with some significant metal deposits and brine springs.

The Hellweg section connecting the towns of Werl, Erwitte and Geseke was part of an important trade route from Aachen to Goslar.

In the fierce Investiture Controversy, Archbishop Frederick I of Cologne in 1102 had occupied and seized half of the territory held by the Westphalian counts of Arnsberg, supporters of Emperor Henry IV.

After the rebellious Saxon duke Henry the Lion was defeated in 1180, Emperor Frederick Barbarossa presented the Archbishop of Cologne, Philip of Heinsberg with these territories and the southwest of the former Duchy of Saxony as the 'Duchy of Westphalia'.

Engelbert of Berg, archbishop of Cologne from 1220, began a campaign to force the nobility in Westphalia into submission and to extract from them the stewardship of the various scattered church lands.

Engelbert managed to connect the lands of the duchy by annexing the territory from Hellweg to Diemel, and secured the south of the Sauerland at Attendorn in 1222.

Archbishop Frederick von Saarwerden began a hopeless campaign to maintain Colognian rights in Marck, and in 1392 was forced to abandon them.