Religious difference was a major cause of the war and the reason cited most often by individuals for their choice of sides. During the 1630s King Charles I’s government had been introducing into the Church of England doctrines and ceremonial that appeared suspiciously Catholic, while persecuting the more-Calvinist or Presbyterian “Puritan” dissenters. Popular fear of Catholicism was amplified by news of massacres of Protestants in Ireland and in Europe where the Thirty Years War was in its most brutal phase. After a Presbyterian-led rebellion in Scotland, the King recalled the English Parliament to vote funds for his army, but Parliament’s refusal led the King to resort to force.
Some re-enactors are drawn to Puritan firebrands such as the preacher Hugh Peters (who had helped found Harvard while exiled in the American colonies), but others redress the balance and portray the established church. I’ve even seen some brave souls portraying Catholics.