In 1649 republicanism became available as a comprehensive political programme. With King Charles dead, the ancient constitution suspended, and ‘a Commonwealth or Free State’ declared, here was a moment to be seized for new-modelling the constitution at home and prosecuting grand designs abroad. Yet, as is well known, the Rump's political timidity restricted constitutional innovation even as it pursued a vigorous foreign policy with the conquest of Ireland and Scotland, and its proposals for Anglo-Dutch union. Republicanism was not responsible for internal renewal, but it did help to inspire external aggrandisement, with paradoxical effects: ‘Nourished by constitutional failure at home, republicanism throve too on military and naval success abroad.’ England may not have become a new Rome by virtue of its constitution, but the infant commonwealth certainly looked set fair to imitate the martial achievements of the ancient republics.

The republican moment of 1649–53– from the declaration of the Commonwealth to Cromwell's forcible dissolution of the Long Parliament – inspired a variety of Englishmen to apply the lessons learnt from the classical republics to their own political situation. John Lilburne, in exile, first read Machiavelli, Livy and Plutarch in these years. In the same period, Marchamont Nedham's The Case of the Commonwealth of England, Stated (1650) and his editorials for the government organ Mercurius Politicus in 1651–2 applied ancient history to modern politics, and drew upon a wide range of classical and contemporary sources to celebrate the successes of the Rump and to point the way forward for republican regeneration.