The counts of Berg emerged in 1101 and became the most powerful dynasty in the region. In 1160 the territory was divided into two portions, one of them later becoming the earldom of Mark. In 1280 the counts moved their court from a castle on the Wupper river to the town of Düsseldorf.
From 1521 the dukes of Berg ruled the duchy in personal union with Mark and Cleves (Kleve). Much of present North Rhine-Westphalia (except for the clerical states of the Archbishop of Cologne and Bishop of Münster) was ruled by the dukes.
The ducal dynasty became extinct in 1609, when the insane last duke died. A long dispute about the succession followed, before the territory were partitioned in 1614: Jülich and Berg were annexed by the Count Palatine of Neuburg, who had converted to Catholicism, while Cleves and Mark fell to the Elector of Brandenburg. Upon the extinction of the senior dynasty ruling the Palatinate in 1685, the Neuburg line inherited the Electorate, and generally made Düsseldorf their capital until the Elector Palatine inherited Bavaria as well in 1777.
The French annexation of Jülich during the French Revolutionary wars separated the two duchies, and in 1803 Berg was separated from the other Bavarian territories and given to a junior branch of the Wittelsbachs. In 1806, in the reorganization of Germany occasioned by the end of the Holy Roman Empire, Berg became a Grand Duchy under the rule of Napoleon's brother-in-law, Joachim Murat. When, in 1808, Murat was promoted to the Kingdom of Naples, Napoleon's infant nephew, Prince Napoleon Louis (elder son of Napoleon's brother Louis Bonaparte, King of Holland) became Grand Duke, and the territory was administered by French bureaucrats. The Grand Duchy's short existence came to an end with Napoleon's defeat in 1813, and in the peace settlement that followed, Berg, along with much of the Westphalian region, was annexed to Prussia, forming a part of the Rhein province.