There is much to admire in this book, not least the author's mastery of the sources in Greek, Persian, Arabic and Turkish with Armenian thrown in for good measure. Nor does he just deal in straightforward narrative texts. His extrication of historical data from Greek rhetorical works is at times masterly. He is alert to all kinds of relevant historical information and processes, which makes his book far more than a straightforward narrative of a neglected period of history. But this should not obscure the fact that the author's main achievement – and it is considerable – is to replace the sketchy and impressionistic treatment of relations between the Turks and the Byzantines in the thirteenth century with something solid and precise.

The puzzle has always been how to explain the rapid loss of western Asia Minor to the Turks at the close of the thirteenth century. Historians have allowed themselves to be guided by the Byzantine historian George Pachymeres (1242–c.1310), who remains the single most important source for this episode. Over his lifetime he had seen the city of Nicaea, where he was born, turn from a flourishing and apparently secure city into a beleaguered outpost. He attributed the swift collapse of the Anatolian frontier in the late thirteenth century to the decision taken by the usurper Michael viii Palaiologos soon after the reconquest of Constantinople in 1261 to end the generous treatment accorded to the borderers (akritai) by the Laskarid emperors of Nicaea. It was, in the historian's opinion, the loyalty, wealth and military proficiency of the borderers which were mainly responsible for the success that these emperors had in holding their eastern frontiers with such apparent ease. Michael Palaiologos's measures against them produced disaffection and eventually defection to the Turks. One of the tasks that Korobeinikov sets himself is to test this interpretation, which has never before been subjected to serious scrutiny.

He follows three main lines of attack: he contends that: (1) the success of the emperors of Nicaea had little to do with their generous treatment of the borderers and can be explained by their Comnenian inheritance; (2) Michael viii Palaiologos's measures against the borderers have not been properly understood and were standard practice; (3) the collapse of the frontier at the end of the thirteenth century was largely the consequence of changes occurring in Asia Minor as a result of the Mongol occupation.

I think that his first point would have carried more weight if the stress had been less on the debt of the emperors of Nicaea to their Comnenian predecessors and more on how much of the Comnenian legacy they were able to rescue from the turmoil of the late twelfth century. It was very much a positive achievement, where improvisation was the order of the day. Just as the emperors of Nicaea were able to restore a modicum of order to the conduct of government, so they brought a degree of stability to the confused and threatening situation that had existed along the frontier with the Turks ever since Manuel Komnenos's defeat at Myriokephalon in 1176. The price was abandoning the key strategic region in the middle Maiander (Menderes) valley around Laodikeia (Denizli) and very probably the middle Sangarios (Sakarya) valley around Malagina too. Thanks to his victory in 1211 over the Seljuq sultan at the battle of Antioch (on the Maiander) Theodore i Laskaris was able to achieve this in an orderly fashion, effectively neutralising Laodikeia and the surrounding region by leaving it in the hands of local leaders, some Greek and some Turkish. Theodore and his successors complemented this by carrying out extensive repairs to the Comnenian fortresses in the border region and by restoring the armies of the themes, which will have borne most of the responsibility for local defence, but we only have George Pachymeres's word for it that the Nicaean emperors accorded generous treatment to the frontiersman (akritai). It is more than likely that their prosperity was a by-product of a period of stability. To that extent Korobeinikov is correct to question Pachymeres's analysis.

He goes on to provide a convincing interpretation of the treatment accorded by Michael viii Palaiologos to the akritai. To begin with, his fiscal measures only applied to a small sector of the frontier covered by the lower reaches of the Sangarios river. It was always the weakest part of the frontier. Korobeinikov argues that soon after the recovery of Constantinople in 1261 Palaiologos instituted a cadastral survey of the region with a view to incorporating the Sangarios borderlands within the regular theme administration. It was in all likelihood very similar to what Manuel I Komnenos had done in the 1150s, when he created the theme of Neokastra further to the south. In other words, Michael Palaiologos was doing nothing out of the ordinary. Korobeinikov provides an impressively detailed account of Michael Palaiologos's defence of his Anatolian frontiers and goes a long way towards exonerating the emperor from George Pachymeres's accusation that he created the conditions that led to the loss of western Asia Minor. Pachymeres is, however, on stronger ground when he attributes a loss of morale among the border populations not to fiscal demands but to a policy of recruiting large numbers of soldiers from Asia Minor – some identifiable as borderers – for Michael Palaiologos's campaigns in the Balkans and Greece.

This partial acquittal of Michael Palaiologos only makes the swift collapse of western Asia Minor after his death in 1282 more difficult to understand. It is all too easy to blame the incompetence of his son Andronikos ii. In the early years of his reign Andronikos took sensible precautions. Not only did he distance himself from his father's religious policies, which had led to the disaffection of large swathes of the Anatolian population, but he also spent nearly three years (1291–3) at Nymphaion – the ancient residence of the Laskarid emperors – in an attempt to recover the loyalty of the local people. But this made little difference because the real problem was the Turkish threat, which the chief minister compared to a many-headed hydra, while Andronikos ii (likened by his patriarch to a toothless lion) was hardly Herakles.

There are two elements to Korobeinikov's analysis of the Turkish threat. The first focuses on the breakdown in the late thirteenth century of effective authority in central Anatolia, which gave free rein to the nomad Turks’ hydra-like tendencies. The second is his identification of the middle reaches of the Maiander (Menderes) and of the Sangarios (Sakarya) as the keys to the control of the frontier. In neither of these areas was there ever a convincing Nicaean presence. The best that can be said is that an understanding with the Seljuqs of Rum and their Mongol overlords allowed the emperors of Nicaea to neutralise them. But, as soon as conditions became less favourable, it was not possible to prevent Turkish nomads flooding in; shunted westwards under pressure from the Mongols. The truth is that in no age have governments had much success in controlling population movements. It has long been realised that the Turkish conquest of the western coastlands of Anatolia was ultimately a result of a build-up of nomads on the western lip of the Anatolian plateau. What the author has done is to give precision to the process. What is more he has done it with, at times, a scintillating display of erudition.