Complex sentence: Marcel's action destroyed the Third Estate's support among the nobles, and the Provost's subsequent support for the Jacquerie undermined his support from the towns; he was murdered by a mob on 31 July 1358.
Split into simpler sentences: Marcel's action destroyed support for the Third Estate among the nobles, and the Provost's subsequent backing of the Jacquerie undermined his support from the towns. He was murdered by a mob on 31 July 1358.