I don't remember exact details and don't have any specific sources, but I remember reading before that one of the Native American tribes/nations (the Iroquois I think) had a big influence on what the government and processes that the Founding Fathers started. How true is this? Did it have more influence than Greco-Roman democratic ideas?
You should check out the Haudenosaunee (Iroquois) Kaianerekowa Hotinonsionne (Great Law of Peace). Several prominent political leaders in early post-contact American History were apparently influenced by it, and some historians argue some of its key principles helped shape the US Constitution (though this issue has been contested by other historians).