Complex sentence: In 1877, after the "Seize Mai" crisis, he was one of the republican majority who denounced the de Broglie ministry, and he took a leading part in resisting the anti-republican policy of which the "Seize Mai" incident was a manifestation.
Split into simpler sentences: In 1877, after the "Seize Mai" crisis, he was one of the republican majority who denounced the de Broglie ministry. He led resistance to the anti-republican policy of which the "Seize Mai" incident was a manifestation.