During times of civic unrest such as riots, the national government can summon the national guard to its help if it thinks that the local forces cannot stop it or if the riots are going out of hand.
Answer:
City-state, a political system consisting of an independent city having sovereignty over contiguous territory and serving as a centre and leader of political, economic, and cultural life.
(I don't know how it spreaded though, sorry :<)
The country's navy uses only imported wood and steel to build itsships.
Low taxes on Roman citizens i belive thats your answer