Book Review: International Relations: Unipolarity and World Politics: A Theory and Its Implications

More than 30 years after the publication of Kenneth Waltz's seminal text Theory of International Politics, scholars are still returning to his theoretical arguments about the ‘structural’ elements of world politics as their major point of departure. Birthe Hansen has joined a number of recent attempts to fill the hole left in Waltz's theory by tackling the structural condition that should not be (at least for Waltz), namely: unipolarity. The classical idea was that given the almost automatic balancing tendencies inherent in the international system, the condition of unipolarity – or the existence of a single superpower – was highly unlikely. At most, right up until the end of the 1990s, theorists thought unipolarity was a sort of transitory phase brought about by the unique condition of the end of bipolarity after the Soviet Union's collapse. A return to the familiar terrain of multipolarity was all but assured; it was only a matter of time.

According to Hansen, however, the time has now well and truly come to theorise properly the current world order and identify the ‘expected patterns of outcomes within the realm of international politics and systemic variations’ (p. 4). Hansen tackles all of the standard neo-realist topics of balancing, competition and stability under conditions of unipolarity. Yet she also goes further to examine the managerial role of a single superpower, almost straying into English School territory. Added to this largely theoretical discussion is a particularly strong empirical chapter on what she terms ‘international challenges’ to unipolarity, including the proliferation of nuclear weapons and terrorism.

Unfortunately, the book largely avoids discussing the ways in which perceptions of polarity affect state behaviour. There is a sense throughout the analysis that the polarity of the system is based almost solely on material capabilities and therefore will be uniformly perceived and understood by all actors. The differing characterisations of the current world order in both the popular and scholarly literature would seem to make this assumption highly questionable. Will the characteristics of a unipolar world that Hansen identifies still play out in a situation where most actors think and act as if they exist instead in a multipolar world (even if the number crunchers obsessed with material capabilities argue to the contrary)?

One of the great strengths of the book is Hansen's focus not just on American primacy but on unipolarity in theory. Nevertheless, the United States plays a starring role in the analysis, particularly in relation to the challenges to international management posed by the current unipolar order. Echoing the prognosis of Stephen Brooks and William Wohlforth's World Out of Balance, ¹ Hansen argues that the unipolar condition will remain with us for some time, since the US edge over any potential competitor(s) is ‘more robust than it appears at first glance; at least measured in terms of time’ (p. 124). She argues that after a brief period of challenge to its leadership, the United States is entering a new period of distinction characterised by ‘the need for the runners-up themselves to invest and develop’ (p. 124).

The book achieves its aim in a clear and largely persuasive fashion, achieving what is perhaps the most thorough theoretical analysis of unipolarity in world politics. If Birthe Hansen's confidence in the consolidation of US pre-eminence is well founded, then her book will be a useful guide for the years ahead.