There were many causes of the British Civil War. The biggest one being religion. King Charles I was a very religious king. He believed that he ruled with the Divine Rights of kings and should be treated very well. He also believed he should be treated with many ceremonies and be treated with lots of worship. Because of this some Protestants (a member or follower of any Western Christian Church) became alarmed because King Charles I was leaning towards Catholicism.
A key factor that also caused The British Civil War was money. Charles's father lived a good and wealthy lifestyle which left the royal treasure empty. The cost of running the royal household for Charles I was too expensive and because of this Charles had to ask to Parliament to grant further taxes from his people. The Parliament refused to grant Charles wish and collect more taxes so he could finance his military.
Another factor was The Long Parliament. The parliament blamed bad advice rather than blaming their king for most of the problems.