I am American in addition to being slightly ignorant, so had no clue (or had forgotten) that King Charles first dissoved Parliament for 11 years, restored it, then declared war on it in 1642, with both sides raising armies. By 1646, Parliament’s centrally organized The New Model Army won the war, arrested the king, won a second civil war against royal loyalists, then executed King Charles in 1649 before declaring Britain a republic. Oliver Cromwell became Lord Protector, ruling Parlimanent much like a king until his death in 1658. After a brief unsuccessful leadership by his son Richard, the monarchy was re-established in 1660.
Oliver Cromwell was much hated in Ireland due to his invasion (and killings of up to 600K people) there, his changes in Parliament were mostly scrapped and he was symbolicaly executed 2 years after his death. He was also a hardliner on Catholics, I believe, and Scotland. His rule may have killed up to 40% of the Irish population. It sounds like he was also instrumental in Parliament’s military victory over King Charles. Oliver Cromwell is considered one of the most controversial (polarizing?) figures of all time in the British Isles.