So, it seems like the general consensus on this board is that Germania around the year 0AD was too undeveloped and sparsely inhabited to be a viable region for Roman conquest and colonization. I am not entirely convinced of this notion, but that is really a subject for another thread. So we'll go with the theory that Germania wasn't suitable for integration into the Roman empire in the mold of Gaul before and Britannia after due to a lack of development in the region. However, this raises the question of when, exactly, Germania reached the level of development necessary to be a viable target for Roman expansion.
I think that, developmentally at least, Germania was at that point by the migration period and the end of the Roman Empire in the West. At that stage the various German tribes had established fairly substantial kingdoms with meaningful institutions so I think the tipping point, again, purely in terms of Germanian development, has to come somehwere in between the two. Conceivably, this developmental threshold may have occurred in different areas at different times. For example, it seems to me that the area ruled by the Marcomanni would have been more suitable for Roman conquest earlier on than other parts of Germany. The Marcomanni certainly seem to have had fairly well organized state structures under Maroboduus and when they fought Marcus Aurelius they were well enough organized to pose a real challenge militarily. To me, those events seem more like the Roman wars with the Dacians than they do the periodic encurions into western Germania to play tribal power politics.
Perhaps the Alemanni's confederation and invasion in the mid 3rd-century represents such a tipping point? They seem to have been relatively well organized, but I don't know if it was more like the migratory invasions of, say, the Cimbri and Teutones and the later Goths, or the wars against the kingdoms of Maroboduus and Decebalus.
So, what do you all think? What are the necessary elements of development for Germania to be a viable Roman conquest? When do you think those elements were present?