Aform of government where political authority rests with a single leader.

The answer would be an absolute monarchy

Explanation:

Allow me to explain some of the terms for government according to the Greek roots the names are based on.  "Kratos" in Greek meant "power" or "rule." There was even a Greek god named Kratos that personified the meaning of power or strength.  So our terms for government are based on Greek compound words about where the power or strength lied in a society.

"Autocracy" means ""power itself" or "himself."  The only one who has power in an autocratic system iss the single leader.

"Democracy" means "rule by the people."  Democratic societies are run by the people.

"Theocracy" means "rule by God."  Societies that follow a religious leadership claiming to speak for God are seen as theocratic.

"Plutocracy" means "rule by the rich." A society where the wealthiest individuals control all the power is plutocratic.

"Aristocracy" means "rule by the noble or excellent ones."  Those who are considered the more elite members of a society govern affairs in an aristocracy.  

There are more such terms, but those are some of the main ones stemming from terms the ancient Greeks gave us.  

declare war, appoint military officers, sign treaties, make alliances