Complex sentence: He demanded the treatment of prisoners in a manner consistent with the Geneva Convention, allowing the detainees to form a grievance committee and was promised a healthier diet for the prisoners after he agreed to end the hunger strike.
Split into simpler sentences: He demanded the prisoners be treated according to the Geneva Convention, allowing the detainees to form a grievance committee. In negotiations, the camp administration promised a healthier diet for the prisoners after he agreed to end the hunger strike.