Complex sentence: Bernard travelled to Chalon in an attempt to negotiate terms, but he and the ringleaders were forced to surrender to Louis, who had them taken to Aix-la-Chapelle where they were tried and condemned to death.
Split into simpler sentences: Bernard travelled to Chalon in an attempt to negotiate terms, but he and the ringleaders were forced to surrender to him. Louis had them taken to Aix-la-Chapelle, where they were tried and condemned to death.