The Roman empire had long assimilated other cultures into a pan Roman identity. This is not a compelling reason, either. Contemporary explanations typically poi

The Roman empire had long assimilated other cultures into a pan Roman identity. This is not a compelling reason, either. Contemporary explanations typically point to two main causes: * The split between the Eastern and western Roman empire caused the comparatively less wealthy Western empire to weaken considerably. Remember, the Eastern Roman Empire didn't collapse and lasted well into the medieval era. * Lower crop yields due to changing climate patterns. Immigration is a symptom of this, lower yields prompting societies to migrate towards more productive areas.