He rose to prominence as a Roundhead officer during the English Civil War. He accompanied Cromwell as second‐in‐command on the invasion of Scotland (1650). He entertained high political ambitions and was chiefly responsible for drafting England’s first written constitution, the Instrument of Government (1653). He supported Cromwell loyally (1653–57), but then resigned all his commissions when his own path to power seemed blocked. In 1662, after the Restoration, he was tried for treason, and spent the rest of his life in captivity.