The primary issue that sparked the English Civil War (1642-1651) was the struggle for power between the monarchy, led by King Charles I, and Parliament. Tensions escalated over issues such as taxation without representation, the king's belief in absolute rule, and religious conflicts, particularly between Anglicans and Puritans. Charles I's attempts to rule without Parliament and enforce religious uniformity angered many, leading to the formation of opposing factions. The conflict ultimately revolved around governance, authority, and individual rights, culminating in a civil war that would change the nature of the English monarchy and parliamentary power.