Preamble to the United States Constitution
The first few words of the Preamble  "We the People of the United States"  were very different than any treaty or law the United States had ever written before.  For example, the United States' first constitution, the Articles of Confederation, describes itself as "Articles of Confederation and Perpetual Union between the States," and then gives a list of all thirteen states.  The treaties the United States had signed were the same.  They were agreements between states, not people.