Cromwell opposed the absolute power of the crown, and when war broke out he became a military organizer for the Parliamentary forces. Realizing the inferior quality of the rebel troops, he organized a 'godly' regiment - the 'Ironsides'. The Ironsides were men of strong convictions who fought with religious enthusiasm.

After the Civil War and the execution of king Charles I, Cromwell became first chairman of the the new republic. He suppressed an insurrection in Ireland (1650) with a severity remembered by the Irish Catholics with bitterness. In the same year he defeated a Royalist army in Scotland, and he fought the Dutch in several naval battles.

In 1653 Cromwell dissolved Parliament and he became Lord protector of the new puritanical republic. As Lord protector he concluded the Anglo-Dutch War, sent an expeditionary force to the Spanish West Indies and destroyed the Spanish fleet at Teneriffe.

In the fall of 1658 Cromwell died, and England fell away from his attempt to realize a puritanical commonwealth of free men.