How did the physical geography of ancient greece encourage the development of city-states?

The principle of checks and balances is based on the notion that

What are the most populous and least areas of russia and why are some areas more heavily populated than others

Quick using the information in the graph, one might speculate that a) w.w.i created increased job opportunities in the u.s. b) the election of president hoover in 1936 caused unemployment to decline. c) the return of soldiers following w.w.ii caused unemployment to increase in the u.s. d) the new deal programs of president roosevelt created employment opportunities in the u.s.