America is often referred to as a democracy, but in truth that is shorthand for a more nuanced reality. America is democratic, but it is also a republic. Democracy and republicanism, though related, are also opposed, much like the American political parties that bear those names.
The signing of the 1787 Constitution of the United States was significant to mankind for a myriad of reasons, not least of which was its innovative application of governance. Perhaps the most ingenious idea put into practice was federalism: the layering of local, state, and national government.