Where did the United States Constitution come from?

Where did the United States Constitution come from?

I don't mean who wrote it, who signed it, or who ratified it.  I mean where did the concept of a republic with separation of powers into an executive, a legislative and judicial  branches of government come from?  Until the US Constitution became law March 4, 1789, no country in the world at that time, or previously, had ever had such a form of government.

Until the US Constitution, there had been only a few governments that were considered republics:  Rome and the Greeks come to mind.  But, neither had what was delivered by our Constitution.

A small body of authority have proposed that a confederation of northeast Indian tribes had a government that closely resembled our Constitution.  But, there was no clear separation of powers, and the confederation had little power to enforce its laws. 

John Adams, in April 1776, wrote a paper, actually a letter to his colleagues, on his thoughts on government.  In it, he proposed a form of government quite like our Constitution.  This was just after the war for independences began, and most citizens of America considered themselves British subjects.  The battles of Lexington and Concord had taken place a year earlier and the leaders of the future United States were about to engage in a struggle of attrition that was to last six long years.  But, John Adams had to come up with the concept, and it doesn’t seem plausible he could come up with his ideas out of the clear blue. http://www.constitution.org/jadams/thoughts.htm

There are some similarities of our Constitution to the constitution then in use in Virginia, and some historians have suggested that the framers of the Constitution started there.  After all, James Madison, considered “the father of the Constitution” was from Virginia.  And, if that is so, where did the Virginians get the concept.  http://en.wikipedia.org/wiki/United_States_Constitution

And in the words of immortal Paul Harvey: “here is the rest of the story”:

Actually, our Constitution, or the principles under which it operates was first articulated, it is believed by most historians, by a Frenchman named Charles-Louis de Secondat, baron de La Brède et de Montesquieu,  or Montesquieu (pronounced: Montiskju) for short (1689-1755).  He was a social commentator and political thinker and is famous for his theory of separation of state powers into an executive, legislative and judicial branches.    http://en.wikipedia.org/wiki/Montesquieu

Most all of the framers of our Constitution would have been familiar with the theory articulated by Montesquieu, and would have had his ideas in mind when writing our Constitution, once they agreed that was the direction they wished to go.