Complex sentence: Having changed sides de Clare shared the Prince's victory at Kenilworth on 16 July, and in the Battle of Evesham, 4 August, in which de Montfort was slain he commanded the second division and contributed largely to the victory.
Split into simpler sentences: Having changed sides de Clare shared the Prince's victory at Kenilworth on 16 July, and in the Battle of Evesham, 4 August, in which de Montfort was slain. He commanded the second division and contributed largely to the victory.