Between the start of the 17th century and the end of the 18th, an Atlantic world took shape. The regions bordering the ocean, in Europe, the Americas and Africa, were all involved in what became, in many respects, a single economic and cultural entity. Commodities and people, as well as beliefs and ideas, moved constantly to and fro across the waters. They included people treated as commodities: African slaves, transported convicts, indentured labourers. As historians have increasingly recognised, it makes more sense to think of this era in terms of the Atlantic's seaways and shores than by way of distinct national or state-centred histories: the English, American, Irish or Jamaican. Yet this was also a world that aggressive, expansionist states - above all, Britain - were trying to control, and one in which modern mercantile capitalism was flexing its adolescent muscles.
The forces of state power and the market economy, including the market in human beings, triumphed in the long run, but they were resisted in a range of ways and by a remarkable variety of people: rebellious African slaves, disgruntled labourers and peasants, dispossessed Native Americans, pirates, proto-anarchists and religious visionaries, mutinous sailors and soldiers, and a few dissident poets and clerics.
This strange array of insurgents was often called "the many-headed hydra" by enemies. In the end, all their attempts at resistance failed, and rapidly disappeared both from popular memory and from the historical record. However, as Peter Linebaugh and Marcus Rediker urge in this passionate effort to resurrect their lost stories, they helped inspire the American and French revolutions, as well as the art of Blake or Shelley, while some of their utopian spirit survives in myriad protest movements today.
So not only is The Many-Headed Hydra about early-modern history; it is also an intensely present-minded, politically engaged work. Both Linebaugh and Rediker are middle-aged Americans, both distinguished scholars, but their book could quite easily be the product of two student revolutionaries, fired with the spirit of May 1968. The romantic leftist historian's celebration of resistance - enshrined in classic works such as Christopher Hill's The World Turned Upside Down (1972) and E P Thompson's Making of the English Working Class (1963) - finds here a glorious late flowering.
In the 1960s, it was possible for Marxist historians such as Hill and Thompson to believe that the 17th- and 18th-century rebels and visionaries they chronicled were not just historical curiosities, certainly not just losers, but bearers of a revolutionary possibility that could still, in the future, be realised. Today, such near-messianic hopes have almost vanished, and Linebaugh and Rediker are writing in a political climate where their kind of romantic, even sentimental, leftism seems isolated and anachronistic. It is no longer easy to argue that their heroes represent the future, as opposed to a long-lost past. Shorn of such dreams, as the embers of 1968 grow ever colder, theirs becomes an act of faith, or a simple cheering on of past, doomed resisters, applauding resistance as an end in itself.
Thus the passions and sympathies that are this book's glory are also the source of its flaws. The authors' attempt to depict 18th-century pirates as politically admirable rebels-with-a-cause is perhaps the least convincing passage, an extreme instance of the recurrent tendency among intellectuals to find countercultural heroes - "social bandits" - lurking within every thug and gangster. One thinks, in particular, of the Ned Kelly legend, which Peter Carey brilliantly reworks in his latest novel, True History of the Kelly Gang (Faber & Faber, £16.99). True, pirate crews often practised a rough-and-ready egalitarianism; and the existence of a few women pirates (just two, in fact: Anne Bonny and Mary Read), some black ones, as well as scattered hints of pirate homosexuality, have set some enthusiasts deep-sea-dreaming about the buccaneering world as a lost paradise of feminism, racial equality and gay rights. But this is all pretty far-fetched, and ignores the evidence of pirates' extreme brutality, sexual exploitation and racism - some pirate crews had African members, but others were enthusiastic slave-dealers.
The Many-Headed Hydra arouses intensely mixed reactions. On one level, it is a piece of soi-disant revolutionary romanticism, its starry-eyed adulation for the mixed bunch of desperadoes, dreamers, doomed rebels and lunatics who are its heroes shading towards absurdity. But on another, surely more important level, it is an impressive exercise in historical reconstruction and imagination: ambitious in its range, vivid and often movingly written.