Enlightenment historians applied the whole culture of their age to the past. At the base of Voltaire's conception of civilization lay the great monarchies of Europe with their institutions, their quests for power, but also their promotion of economic welfare, the basis of cultural progress. Voltaire believed in the republic of scholars and in the primacy of ideas in historical evolution. Ideas were the motive force. Human nature reveals itself only in historical evolution.
Progress is the gradual assertion of reason.
To some degree, this was didactic history. Hume also accepted the uniformity of man and failed to grasp the irrational factors in human history. But he too asserted the primacy of ideology. Yet this static view began to change. Hume, of course, was horror-struck with Voltaire's sweeping generalizations.