Complex sentence: Agnes retired to a convent, and the government was placed in the hands of Anno whose first move was to back Pope Alexander II against the antipope Honorius II, whom Agnes had initially recognized but subsequently left without support.
Split into simpler sentences: Agnes retired to a convent, and the government was placed in the hands of Anno. His first move was to back Pope Alexander II against the antipope Honorius II, whom Agnes had initially recognized but subsequently left without support.