Montesquieu published The of Spirit of the Laws in 1748. One of its main points is that in order to foster true political liberty, the judicial, executive, and legislative branches of government must be able to check each other. Without the existence of these checks, one branch can tyrannize the others, resulting in the loss of political freedom for the citizens of that nation.
This concept was crucial in the framing of the United States Constitution about a half century later. It seems to have worked pretty well in the United States. In fact, it might be working so well that we can blame it for what is often called “Washington gridlock” these days. Not much seems to be getting done because the various governmental entities are effectively blocking each other. Here's an actual quote from The Spirit of the Laws:
“Were the executive power not to have a right of restraining the encroachments of the legislative body, the latter would become despotic; for as it might arrogate to itself what authority it pleased, it would soon destroy all the other powers.”
For Montesquieu the “despotic” form of government was to be avoided at all costs, because its power was unchecked. The despot in charge might get a lot done, but at the expense of the political liberties of everyone else. Montesquieu is warning us not to fall into such a tyrannical trap.