Final answer:
The two sides fighting in the English Civil War were the Royalists, who supported the king, and the Parliamentarians, who supported parliament.
Step-by-step explanation:
The two sides fighting in the English Civil War were the Royalists (who supported the king) and the Parliamentarians (who supported parliament). The Royalists, also known as Cavaliers, supported King Charles I, while the Parliamentarians, also known as Roundheads, supported the authority of Parliament.