The theory about underlying modern democracies was developed to challenge the idea that

The correct answer is: "those of royal birth have absolute authority to rule"

The Enlighment movement emerged in Europe and developed the philosophical base of modern democracies. It was formed by the contributions of thinkers that promoted freedom and reason over medieval superstition and religious dogmas, and the establishment of democratic societies where the power resided on its people that could elect representatives, and not in absolute monarchs or tyrant rulers who inherited the power from their ancesstors. It was believed that the power of these medieval kings had been granted by God and that it was unchallengeable.

The resulting states that emerged based on the principles of this movement, enacted bills of civil rights for the first time in history, and implemented principles such as the division of powers or the social contract, through which citizens elected their governors by suffrage.