While this book ranges widely, both chronologically and geographically, at its heart lies the bitter war in which Ethiopia and Eritrea fought for possession of the border area of Badme in the late 1990s. Richard Reid has written elsewhere of his frustration at some of the explanations that have been offered of that conflict. Sometimes mocking (‘two bald men fighting over a comb’) and sometimes personalized (tending to focus on the troubled character of Isayas Afeworki, Eritrea's President), these have been overwhelmingly concerned with the present. Reid's concern is to set the conflict in perspective, and he argues that the war over Badme was only the most recent event in a lengthy history of violence which stretches back for centuries. He winds the story of this ‘fault-line’ of tension in with many other such stories, taking his readers from Somalia to eastern Sudan; insisting all the time that while new kinds of weapons, and new kinds of international interference, may have exacerbated conflict in the region, they have not been its fundamental cause. Those causes, Reid insists, lie in divisions in the region itself.

These divisions are sometimes characterized by Reid as multiple fault-lines, but more consistently he describes them as frontiers: sometimes productive, often chaotic, at the margins of power but always helping to shape both how power was exercised, and by whom. The frontier that concerns Reid most runs on an uncertain line through the northern highlands of Ethiopia, which now has taken international form in the Ethiopia–Eritrea border. But there are many others, some topographical, some ethnic and linguistic, some religious. There are frontiers between highland and lowland along what is now the Sudan–Ethiopia border; in the arid lands of what is now north-eastern Kenya; in the Ogaden, between Somalia and Ethiopia; through the highlands of southern Ethiopia between Oromo and Amhara; in central/northern Ethiopia between Shoa and Tigre; and everywhere, across the region, between Christian and Muslim. Reid argues that the violence which has characterised attempts to control these frontiers has fed back into the cultures of the region, and that the consequence has been a profound and long-term militarization. He has limited patience for those who argue that ethnicity is powerful only because it has been instrumentalized by those who seek power; on the contrary, he suggests, ethnicity has been instrumentalized because it is powerful and enduring, and is the vital force in many of these frontiers. On this, as on other issues, Reid is deft in his summary and critique of existing literature, admirably combining wit with brevity and clarity, and delivering some caustic comments on nationalist imaginings.

Quite how far back these conflicts may be traced is perhaps unclear. The title of the book mentions 1800, and the chapter on the zemene mesafint of the eighteenth and early nineteenth centuries suggests that this period of violent competition for power between multiple princes set the enduring pattern. Elsewhere, though, Reid hints both at an even longer genealogy, and at the particular significance of the centralizing ambitions of the mid-nineteenth-century Ethiopian emperor Tewodros. The repeated mention of increasing violence does reach a point where one wonders quite how violent things could be: having heard of the ‘vicious total war’ of the zemene mesafint, the reader may wonder how to compare this with the reported high levels of violence of the mid-twentieth century. The absence of much specific detail is perhaps a weakness here – without wishing for gruesome details, it would be useful to get a sense of how thoroughly, and in what ways, violence had permeated human relationships, and how far there were changing moral bounds to the use of force. But the overall point is clear: a political culture of violence developed, driven by experience on the region's multiple frontiers, and this has shaped politics and driven further conflict.

Ambitious in its coverage, the book is inevitably uneven. It is at its strongest in discussing the long conflict in northern Ethiopia, and there is quite a lot of narrative detail on the high politics of the Ethiopian state that will seem familiar to scholars of the region; by contrast, the material on Somalia and the Sudan frontier is quite brief. There are some marvellous epigrams – on the deep history of Ethiopia, Reid says ‘I do not perceive a continuous state, but rather a continuous state of violence’; and he refers elsewhere to ‘shifta statehood’. But the latter term is not very fully explored, and there are some analytical loose ends left hanging in the narrative rush to the present. Did new ideologies of revolution change the nature of violence? Was the ‘violence’ of popular resistance to the state (which Reid suggests was a new element in the region from the 1950s) different to the violence of the ‘shifta state’? And some readers may question the explanatory power of the idea of the frontier: there are evidently many frontiers in the region, of many kinds, but that does not make this region unique, nor does it explain why some of these frontiers have been so consistently violent, and others less so. Overall, though, this is a book which displays an immense knowledge of the region, and an admirable insistence that the people of the region – and their conflicts – should be understood on their own terms, and in the context of their own history.