D. lack of a central authority and infrastructure
The development of the manor system in Western Europe after the fall of the Roman Empire was primarily influenced by the absence of a strong central authority and the decline of infrastructure. This power vacuum led to localized forms of governance and economic organization, resulting in the establishment of manors as self-sufficient units of agriculture and society. The other factors were important as well, but the lack of centralized authority and infrastructure was the most significant contributor to the emergence of the manor system.