There are many forms of government: monarchy, oligarchy, democracy, republic, anarchy.  And today many speak of the "far left" (communism) or the "far right" (facism).  Very simply our founders considered the two extremes to be ANARCHY on the one hand and TYRANNY on the other, either no government or total government.  

What they constructed was designed to put power with the people assembled in local venues, and provide tools to allow the people to keep government in check.  This was a republican form of government that protects our unalienable rights.

This presentation covers democracy vs republic, de jure vs de facto, sovereignty, and the five branches of government.