The idea of migrations being caused in the ancient world by some combination of overpopulation and military pressure has a long pedigree. It comes up in discussions about the Gauls, Goths, Vikings, Slavs, and often blames other groups such as the Huns for precipitating the crisis. However, in the modern world we dont ever really see overpopulation as a factor, and refugees, despite what some right wing elements would have people believe, do not constitute an invading army.

In this particular case, trying to pin the seeming surge in Germanic incursions on pressure from the Goths makes a certain sort of sense. However there are a number of issues with this idea. Firstly, the Goths' origin and subsequent migrations across Eastern Europe before invading the Roman Empire while fleeing from the Huns, is likely an embellishment or outright fabrication. That's not to say that people, including later Goths, did not believe it to be true at the time, but any effort to reconstruct a firm Gothic identity for the Germanic element of the Bkack Sea culture around the late 4th century is doomed.

So what are other more likely explanations? Well the number one factor in migratory movements is always economics and opportunity. Despite Roman border guards and fortifications, the division between the Roman and the barbarian worlds was somewhat porous, with a significant amount of men and material making their way back and forth. This could take the form of trade and merchants going from one side to the other or it could be young men going across the border to earn their living, either by raising or perhaps by service in the army. By this time in the Empire there was a long history of cooperation as well as conflict between various Germanic groups and the Romans.

We shouldnt imagine, no matter what ancient sources tell us, that these incursions were the result of fully fledged national groups with a distinct social structure and history. Identity among these groups was much more fluid in practice and could shift. The idea that entire gens of the Marcomomanns, or Iazyges, or any other group were capitalizing on Roman weakness to invade and expand their kingdoms or realms, or seek a new homeland away from their persecutors, is utterly anachronistic.

And yet, based on the sources availible, clearly something went different from the normal state of affairs and the incursions into Roman territory became far more violent than cooperstional. Even if these movements and incursions werent the result of Gothic pressure, what were they? It's very difficult to arrive at a firm conclusion given the biases of our only sources, but based on earlier and later migratory movement in the region we can perhaps hazard a hypothesis. With Roman power looking weaker due to the plague and wars in the East as well normal issues along the German border, perhaps the calculation within the minds of those Germans seeking economic advancement changed a bit, suddenly working for or with the Romans became a little less appealing and raids and attacks started to look like the better pay off.

We shouldnt look at these groups and wonder why they didnt defend their homelands from the Goths, they were likely a rather limited factor in the decision to raid and harass the German border rather than keep the more sedate status quo. Instead we should wonder what factors led these people to change their relationship to Rome into a far more outright hostile one, and how they were able to bring this about.