Parliamentarian Forces were military groups that supported the Parliament of England during the English Civil War (1642-1651). They opposed the Royalists, who supported King Charles I. The Parliamentarians aimed to limit the power of the monarchy and promote a more representative government. Key figures in the Parliamentarian Forces included Oliver Cromwell, who emerged as a prominent leader and military strategist. The forces were known for their disciplined troops, particularly the New Model Army, which played a crucial role in defeating the Royalists and ultimately led to the establishment of the Commonwealth of England.