limited government

Anyone who thinks seriously about the American Constitution begins with the idea of "limited government".  In a constitutional democracy power is divided among three groups. Each group, or "branch"  has a unique and separate function.  The first group makes laws, the second group enforces laws, and the third group, interprets laws. Power is divided. One branch checks the other, one branch limits the other, and so on.
Constitutional government is a system for controlling or limiting political power.