It's been asserted, and then laughed at by conservatives, that the Constitutional system came from the model of the Iroquois confederacy....the only problem, for these armchair pundits of the right, is that it's probably true. At least somewhat.
Let me explain.
In all probability, first off, it was the form of government under the Articles of the Confederacy, not the Constitution, which would have been influenced by the Iroquois Confederacy. The radical democrats who formed the Articles and the revolutionary state governments after the war was won were the people who were interested in Native American examples of government, not the Framers of the Constitution.
Example: Benjamin Franklin, who had an active interest in Native American government and who was one of the authors of the Albany Plan of Union, which prefigured the Articles more than the Constitution, I would argue, was only at the Constitutional Convention in Philadelphia as a ceremonial gesture, and did not participate. Jefferson was out of town as the ambassador to France.
Now, why would I say that the radical democrats back then would have been interested in Native American forms of government? For the same reason that radical democrats today are. Radical democrats back then saw society as a confederation of different groups starting from the family and working their way up to that 'state' or the, ugh, 'nation', and believed that whatever top level entity existed got it's legitamacy from the bottom, not the other way around. To people who think like that the example of the Iroquois Confederacy is really interesting, because it was a Confederacy of five tribes, I believe, who came together for collective decisionmaking in a formal structure every year yet had no central government.
Here, then, is an example of radical, decentralized, democracy from the bottom up in action. This no doubt is what the people who studied it back then saw as well, even more so since books like "Politica" by Althusius, the author who expressed the philosophy of the democratic (yet religious as well) Dutch Rebellion in the 16th century, explicitly spelled out the sort of semi-tribal confederal basis of society which I'm talking about.
People look at Anthropology today for insights into society and how society could be different; people looked at Anthropology back then for the same insights, although they didn't call it Anthropology then.
But.....it's the Articles of the Confederacy not the Constitution.
The Constitution was a document written by people who really didn't like democracy. It was subsequently gutted and turned around by the Jefferson administration and the Democratic Republican presidents which followed it to be somewhat sane, but that doesn't change the fact that when it was put in place it's aim was pretty far from what the goals of someone seeking to imitate the Iroquois Confederacy would've had.