Locke, Montesquiue and the Roman Republic. The DoI is a Lockean political manifesto, not a traditional Christianity-inspired document. Locke did not acknowledge any government as deriving its authority from God. He believed that all government is a social contract created by men and women for the mutual defense of their lives, liberty and property. He believed that there exists no innately legitimate authority because no one could make a legitimate claim to being Adam's heir who was alive in 1692 or today.
It certainly wasn't from the rebirth of civilization after the dark ages, because it was at that time that men regarded sovereignty as coming from God.
Decartes, Locke, Spinoza, etc derived more of their philosophical views from ancient Roman and Athenian civilization than Christian civilization. Cogito ergo sum is something that Artistotle, Plato or Socrates would have argued. Such a sentiment borderlined on heresy. Locke's insistance that government rules by the consent of the government harks back to the Athenian and Roman Republics, not the Bible.