A surprisingly compelling story of how the Anglo-Saxon kingdom of Northumbria, through it's adoption of first Celtic and then Roman christianity. emerged from warlordism to become an institutional monarchy.
There simply aren't sufficient documentary resources to support this historical narrative, so Adams presents each chapter as if it were an episode of Timeteam; with contributions from archeology, landscape studies, history, and even literary criticism. The latter comes in the form of Adams' critical reading of Bede's Ecclesiastical History - he argues that Bede needed to create a compelling narrative of God's providence to his one church, and selected his evidence accordingly.
The biggest loser in this process was the indigenous British Church which had hung on after the departure of the legions. For Bede the failure of the British Church to convert the incoming Anglo-Saxons (and it's rejection of Augustine's mission) made them more perfidious than the incoming pagans. So the significance of the British contribution to the formation of the English church is played down in favour of the proselytizing Irish and Roman Churches. A early victim of this is cautious Edwin, the first Christian king of Northumbria, albeit one who was converted by the British while in exile in Anglesey, and later ally of the British King of Gwynedd.
Which highlights another position that Adams takes against Bede's narrative - that there was no hard distinction between Briton and Anglo-Saxon; Britannia's dark age leaders were equal opportunity warlords. Equally likely to ally or attack across ethnic and religious boundaries. This is explicable, I suppose, because Adams also believes there was no mass immigration of Britain by Anglo-Saxons; that the genetic and landscape evidence does support this traditional historical account. We had instead an exchange of elites, rather like the one that happened after the Norman conquest, albeit in a more ragged fashion. This view, however, still has to account for the disappearance of the British language across most of Britain.
Edwin's nephews were raised on Iona in the Irish monastery there, and when one of them, Oswald became king he invited his Irish mentor Aidan to found a similar monastery on Lindisfarne. The Irish church with its enthusiasm for asceticism and missionary work was much more to Bede's liking, and so played a bigger part in his Ecclesiastical History. And we can perhaps argue that it is of more importance to the institutional development of the Church of England, because it had a tradition of anointing those it recognised as king. So the king supported the monasteries and the monasteries supported the king, which made both kingdom and church much more stable than they had been when legitimacy was conveyed purely by military success. So much so, that Oswiu, Oswald's brother became the first Northumbrian King to die in his bed.
In the most interesting part of the book, Adams goes on to argue that the monastic movement was too successful. It created a Northumbria that was economically successful and politically unassailable, but one that became militarily weak and ultimately susceptible to external attack. Those rich monasteries became the first targets of the Vikings, less than 200 hundred years after their foundation.
Adams proposes the following mechanism for this. Previously the King gifted land in exchange for military service, when a particular warrior was killed in battle, the land came back into the king's hands to be allocated to a new warrior. So the kingdom's wealth and strength were kept in sync. When the King gifted land to a monastery - in posterity, it no longer came back into the king's hands, and it no longer contributed to the military strength of the kingdom. The monasteries were able to plough their surpluses back into their lands, this investment increased the wealth of the monasteries, but not the strength of the kingdom. Eventually for the nobility, sending your son into a monastery became much more attractive than sending him into battle. When St Wilfrid, bishop of Northumbria died he was possibly the richest man in Europe.
What I find so interesting about this mechanism, how the adoption of Christianity upset the balance between blood and treasure, is its potential to be applied to other places and other times. Certainly, was it not the reason Anglo-Saxon, Irish and Pictish pirates flocked into Britannia after the legions left. But could it not also explain the general collapse of the Roman Empire? And should it not be a warning to Europe today, surrounded by warlordism to the south and east, and dependent on its American overlord for its military protection?