Complex sentence: The passage of a law that required the peasants to defend the "châteaux" that were emblems of their oppression, was the immediate cause of the spontaneous uprising; it was particularly onerous as many commoners already blamed the nobility for the defeat at Poitiers.
Split into simpler sentences: The passage of a law that required the peasants to defend the "châteaux" that were emblems of their oppression was the immediate cause of the spontaneous uprising. It was particularly onerous as many commoners already blamed the nobility for the defeat at Poitiers.