Complex sentence: However, his past association with Cromwell and the execution of Charles I eventually drew his fortunes to a close when Charles II began to regain full power of the monarchy and began to strike out at everyone who had a hand in the execution of his father.
Split into simpler sentences: However, his past association with Cromwell and the execution of Charles I eventually drew his fortunes to a close. When Charles II began to regain the full power of the monarchy, he also began to strike out at everyone who had a hand in the execution of his father.