Robert Brenner offers a socio-political account of the transformation of English commerce in the century after 1550 and a socio-economic explanation of the political alignments of the London merchant community in the conflicts of the early Stuart period. In a major reinterpretation of long-term commercial change, he demonstrates that new possibilities in the import trades--more so than problems in the traditional cloth trade--were behind the foundation of the long-distance commerce to the east. He shows, in turn, the way in which social groups of great City merchants wielded organizational and political power to exploit the emerging commercial opportunities. Brenner demonstrates the enormous significance of merchant politics for national political development from 1621 to 1653. He brings out, in particular, the decisive roles played from 1640 by London's great company merchants in support of the crown and by a new social group of entrepreneurs--the politically radical and militantly Puritan traders who developed the colonial plantation commerce--in support of the parliamentary leadership. The new colonial merchants assumed great national influence with Cromwell's victory, becoming the chief architects of the Commonwealth's dynamic commercial policy.