Parliament's most radical faction, led by Oliver Cromwell, seized control by expelling over 140 royalist MPs, dubbed "Pride's Purge," to pave the way for the High Court of Justice to put King Charles I on trial for treason. In a bold move, Colonel Thomas Pride and his regiment blocked the stairs of the House of Commons, arresting and excluding members deemed loyal to the monarch. This coup allowed the reconstituted Parliament to orchestrate the King's trial, which would eventually lead to his execution in 1649.