Thearchy or theocracy is government by the immediate direction of God though his ministers and representatives.
When Christ comes to reign personally on the earth during the millennial era, a perfect theocratic government will prevail.
This perfect system of government was set up by Adam, and to a great extent by Abraham, Isaac and Jacob. Certainly ancient Israel in the days of Moses and the judges operated on a theocratic basis.
Man cannot operate such a government unless it is under the direction of God. All governments today are far removed from God and rely on their own wisdom.