The Roman empire tends to be seen as a whole whereas the early middle ages tends to be seen as a collection of regional histories, roughly corresponding to the land-areas of modern nation states. As a result, early medieval history is much more fragmented, and there have been few convincing syntheses of socio-economic change in the post-Roman world since the 1930s.
In recent decades, the rise of early medieval archaeology has also transformed our source-base, but this has not been adequately integrated into analyses of documentary history in almost any country.