Complex sentence: However, these were rumors spread by John's enemies to discredit him as a weak and grossly irresponsible ruler, given that at the time John was engaging in a desperate war against King Philip of France to hold on to the remaining Plantagenet dukedoms.
Split into simpler sentences: However, these were rumors, ignited by John's enemies to discredit him as being a weak and grossly irresponsible ruler. Given that at the time they were made John was engaging in a desperate war with King Phillip of France to hold on to the remaining Plantagenet dukedoms.