nomocracy

from The Century Dictionary.

• noun A system of government established and carried out in accordance with a code of laws: as, the nomocracy of the ancient Hebrew commonwealth.

from the GNU version of the Collaborative International Dictionary of English.

• noun Government in accordance with a system of law.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun politics a political system under the sovereignty of rational laws and civic rights.