The history of empires and the history of oceans have been two of the most vigorous and fertile strains of historiography in recent years. On the face of it, imperial history and maritime history have much in common. They are both transtemporal, in that they are not tied to any specific period and can be pursued across vast expanses of time. They are also both transnational, because they are not confined to nation-states and must be followed over great tracts of space. Neither has been limited to the study of Europe, or even to the period of European activity in the world beyond Europe. Indeed, some of the most challenging recent oceanic histories have been written by pre- and ancient historians: for example, Peregrine Horden and Nicholas Purcell’s wonderfully multifaceted study of the pre-modern Mediterranean, The Corrupting Sea: A Study of Mediterranean History (2000) or Barry Cunliffe’s richly expansive Facing the Ocean: The Atlantic and its Peoples, 8000 BC–AD1500 (2001). Similarly, the study of empires has been the province of archaeology as much as of history, and extends from some of the earliest human societies in Mesopotamia all the way up to the near-present and the quasi-imperial ventures of contemporary powers in the same region.

The histories of empires and oceans intersect and overlap but they are far from identical. Imperial history treats the complex, often multiethnic, polities in which dominant elites have exerted central control over territory, population and resources. By contrast, oceanic history deals with connections and circulations outside centres of control and calculation and usually beyond the limits set by particular national histories. The competition of empires did shape the histories of the Mediterranean, the Atlantic, the Pacific and the Indian Oceans, but so did other forces like commerce, navigation and climate. Oceans were important theatres of imperial activity, but they were not the only such arenas. Even sea-borne empires like the Dutch and the English were territorial entities before they became maritime enterprises, however small the territorial core of the empire was in comparison with the geographical reach of their fleets and settlers. Empires have waxed and waned, but oceanic basins have shifted mostly in the perceptions of the agents who traverse and imagine them. Moreover, empires have tended to operate outward from sovereign cores surrounded by moving frontiers and marchlands.