The Civil War The Civil War was caused by a dispute over the power of the king against Parliament in the 17th century.The Roundheads led by Oliver Cromwell wanted to abolish the monarchy and to reassert the rights of Parliament,but royalists wanted the monarchy to go on.In 1642,the royalist armies were defeated and King Charles I was executed in 1649. The Civil War The Civil War was caused by a dispute over the power of the king against Parliament in the 17th century. The Roundheads led by Oliver Cromwell wanted to abolish the monarchy and to reassert the rights of Parliament, but royalists wanted the monarchy to go on. In 1642, the royalist armies were defeated and King Charles I was executed in 1649