Almost all European aristocracies develop out of power and wealth gained from owning land. This was not the case everywhere. Changes in middle ages modulated the meaning of both military power and land holding. But the aristocracy remained. B. Availability of goods Luxury good become available - Spices, Silk, or even good woolen cloth, Wine.
Aristocracies are a consuming class.
Old self-sufficiency was not appropriate to their status. In early middle ages no distinction between a monarchs private income and public expenditure. It was possible to run a state on that. Government did very little. As society becomes commercialized, money becomes more important.