The population of America is already divided as it is. Every day I listen to socialists disagree with capitalists and vice versa. Trying to force everyone to work under ONE system is terribly inefficient and leads to problems. It seems allot more "free" to have America's divided people form their own governments according to how they want to live and letting others do the same. Mimicking the Iroquois confederacy and letting people CHOOSE how THEY want to live and giving them OPTIONS will help with this whole left-right division in the United States.
Besides, if you try to impress everyone... You impress no one. Plus unity does not come ONLY through having everyone under one system. Unity can come through separate systems that each satisfy their own people working together towards a common goal.
Also having a bunch of smaller governments control smaller areas will allow the interests of the people to become more represented.
I do believe the U.S. tried the whole "smaller nations working together" thing once, under the Articles of Confederation. It turned out horribly. Like a bunch of smaller U.S s, with a lot less resources, and all wanting more. Unity is, quite simply, in everyone's best interest. I vote for one big thing.