Answer: The Spirit of the Laws.
Some extra relevant information:
The concept of “separation of powers” originates from a renowned work by the French philosopher, Charles-Louis de Secondat, Baron de Montesquieu. In his influential book, “The Spirit of the Laws,” published in 1748, Montesquieu expounded upon the idea of dividing governmental powers into separate branches. This principle serves as a cornerstone of modern democratic systems, ensuring a system of checks and balances, as well as preventing the concentration of power in the hands of a single authority. Montesquieu’s work continues to shape political thinking and the structure of governance in numerous countries around the world.