Oliver Cromwell set up a republic called the Commonwealth of England (1649–1660) which he ruled after the overthrow of King Charles I. James Harrington was then a leading philosopher of republicanism. John Milton was another important Republican thinker at this time, expressing his views in political tracts as well as through poetry and prose. In his epic poem "Paradise Lost", for instance, Milton uses Satan's fall to suggest that unfit monarchs should be brought to justice, and that such issues extend beyond the constraints of one nation. As Christopher N. Warren argues, Milton offers “a language to critique imperialism, to question the legitimacy of dictators, to defend free international discourse, to fight unjust property relations, and to forge new political bonds across national lines.” This form of international Miltonic republicanism has been influential on later thinkers including 19th-century radicals Karl Marx and Friedrich Engels, according to Warren and other historians.