Simplify the following text for a Grade 11 native English-speaking person.
Original: The opposition of the rebellious German nobles used the excommunication of Henry to set up a rival king Duke Rudolph of Swabia ( Forchheim , March 1077 ) .
Simplified: That the excommunication of Henry IV was simply a pretext for the opposition of the rebellious German nobles is transparent . Not only did they persist in their policy after his absolution , but they took the more decided step of setting up a rival ruler in the person of Duke Rudolph of Swabia ( Forchheim , March 1077 ) .