Complex sentence: After Napoléon's ultimate defeat (Battle of Waterloo), Fouché again started plotting against his master and joined the opposition of the parliament (after the defeat of Waterloo) and headed the provisional government and tried to negotiate with the allies.
Split into simpler sentences: After Napoléon's ultimate defeat in the Battle of Waterloo, Fouché again started plotting against Napoleon and joined the opposition of the parliament. He headed the provisional government and tried to negotiate with the allies.