Actually there are many references that we are NOT even founded as a "Nation".
We are a Federal Constitutional Republic comprising fifty states, and each state was meant to be sovereign and there was expected to be many "nations" within the states. (Cherokee Nation, etc...)
What we are bordering on now due to the massive intrusion by the unlimited power of our centralized government is the singular "United State".
The Pledge of Allegiance was a tipping point where the idea of "one nation (under GOD none the less)" took firm hold. This is a HUGE mistake because we are many nations (and some people don't believe in God). If all Atheist had a similar culture they could be their own nation as well. The only thing that we should be able to agree on is "liberty and justice for all" which was the purpose of the pledge (united for liberty). Only later religious collectivists added (under God). (Once upon a time the requirement to be American was to denounce the king and pledge allegiance to the Constitution).