If you’re talking about the US, a constitutional bicameral presidential republic, with three branches and a judiciary of your peers, was first done in the US. In fact most modern constitutions are inspired by the American constitution.

• Republic - Greece and Rome.
• Democracy - Greece
• Judiciary & Jury - Saxon/England
• Common Law Legal System - Saxon/England
• Principles of the Enlightenment that inspired the Founding Fathers - Germany, France, Italy and England

More countries have used the Canadian constitution than the US as their framework.