Which early american culture was one source of inspiration for the structure of present-day united states politics?

The Iroquois Confederacy, which consisted of the Oneida, Onondaga, Seneca, Cayuga, Mohawk, and Tuscarora nations, established an elaborate and sophisticated system of representative government, one that exists to this day and very likely existed well before Columbus stumbled upon the Americas. This system of government, called The Great Law of Peace, even has its own constitution, which was originally memorized and recited orally rather than written on paper.

In one instance in 1744, at a treaty council between the Iroquois and the colonies of Pennsylvania, Maryland, and Virginia, an Iroquois leader named Canassatego strongly advised the American colonies to unite under a common government modeled on the Iroquois system. Ben Franklin admired Canassatego's speech so much that he printed it and distributed to cities all over America and Europe. Ben Franklin then proposed a unified colonial government at a gathering of colonial leaders a couple years later, calling it the Albany Plan of Union. That plan failed, but a similar plan (the U.S. Constitution) eventually succeeded.