When I was a child, and for a hundred years previously, the model of change in prehistoric Europe was one of ethnic replacement. For example, that the change from stone to copper and then bronze technology or the change from Romano-British to Saxon, was about a new ethnic group coming into England and driving out the old inhabitants en masse. This tribal migration narrative fed into colonialism, and was also used in central Europe as a way of differentiating the new nation states.
More sophisticated methods, including DNA analysis, have proved this model of prehistory largely false, and the consensus has move away from it. Nowadays people feel that change is more to do with the drift of technology and language and beliefs through relatively static populations (with some immigration, and sometimes replacement of rulers). However Heather's argument in this book is that in certain cases mass population migration can be significant, and he thinks the intrusion of the Huns into Europe set off destabilising population shifts which hastened the end of the Empire - without in any way endorsing the old ethnic model.
I am interested in the collapse of societies and what it feels like to live through that. I guess a lot of people are nowadays, for obvious reasons. Heather argues that Europe was initially strongly differentiated between barbarian and civilised zones, and this set up a tension which could not be maintained. Analogously to thermodynamics, the hot areas got cooler, and the cold areas warmed up, until Europe was undifferentiated. So it was less of a collapse than a move to equilibrium.
On the final page he says:
'Even without the Huns these processes of development would eventually have undermined the Roman Empire... what emerges from the evidence is that living next door to a militarily more powerful and economically more developed imperial neighbour promotes a series of changes in the societies of the periphery, whose cumulative effect is precisely to generate new structures better able to fend off ... imperial aggression.'
This is exactly what I think. Further down the page.
'The way that empires tend to behave, the mixture of economic opportunity and intrusive power... prompt responses from those affected which in the long run undermine their capacity to maintain the power advantage... whether you find that comforting or frightening will depend on whether you live in an imperial or peripheral society.'
People don't set up a rival empire, they fray away at the edges. And nowadays in my opinion those edges are not geographical, and the excluded are not far away: they are inside our culture, creating a new one which will be able to resist it (for good or bad).