Which of the following authors is credited with promoting the concept of separation of powers in government?

The correct answer is Montesquieu, who is notably recognized for his influential work in political philosophy, particularly in the context of separating governmental powers. In his seminal book "The Spirit of the Laws," Montesquieu articulates the idea that the best way to prevent tyranny and protect freedom is to divide governmental authority into distinct branches, each with its own responsibilities and powers. This concept of separation of powers laid the groundwork for modern democratic systems, especially influencing the structure of the United States Constitution.

Montesquieu argued for three branches of government: the legislative, the executive, and the judicial, each acting independently yet interdependently, providing checks and balances on one another. His insights have significantly shaped the development of Western political theory and governance.

The other authors listed have made substantial contributions to political thought, but their focus does not center on the separation of powers in the same way that Montesquieu's does. Voltaire is primarily known for his advocacy of civil liberties and criticism of authority and religion, while Rousseau's work frequently discusses the social contract and general will rather than the specific division of government powers. John Stuart Mill is best known for his ideas regarding liberty and utilitarian philosophy, rather than the structural organization of government.