Jülich(-Berg) was a county (later duchy) in the HRE. In 1376 the last count of Berg, Gerhard died, and his lands were united with Jülich.
During the Twenty-Year War, 1493, the former monk Karl Koch who read a bit too much about the Roman republic during his time as library assistant in the monastery, started as a "soap box preacher", declared the "Rheinische Republik" (republic of the Rhine), which was soon defeated by the duke of Jülich-Berg, however. Thus, he acquired the electorate of Cologne quite peacefully, and would control the bishop of Cologne from now on.
Since 1553, the successors of Walram IV had to govern the duchy together, which wasn't always easy. In 1638, Engelbert IV had to be removed from government by his relatives.