Complex sentence: On top of his military position Monck was in a particularly powerful position because of his former relationship with and endorsement from Oliver Cromwell, many imbued him with the power to affect who the next king would be.
Split into simpler sentences: On top of his military position Monck was in a particularly powerful position because of his former relationship with and endorsement from Oliver Cromwell. Many imbued him with the power to affect who the next king would be.