Complex sentence: Perceiving that there were divisions in the ranks of his opponents between Catholic and Protestant, Fleming and Walloon, he skilfully set to work by persuasion, successfully taking advantage and fomenting the growing discord, and bring back the Walloon provinces' allegiance to the king.
Split into simpler sentences: Perceiving that there were divisions in the ranks of his opponents between Catholic and Protestant, Fleming and Walloon, he skilfully set to work by persuasion to take advantage of the divisions and foment the growing discord. By doing so he was able to bring back the Walloon provinces' allegiance to the king.