My knowledge about this topic comes from a single source[0], but your argument also seems to apply to Venice. It found its beginnings as Rome was being sacked, when people fled the invaders and found safety on the islands. With political knowledge and sophisticated technology, they displaced (and integrated) the 'native' people and built an incredible civilization. Venice went on to become a significant power, greatly aided by geographic advantage.

Also, it's interesting to consider the decline of Venice. Although that's better described by cliodynamics than geography.

[0] Venice (Wonders of Man Series), John H Davis http://www.amazon.com/Venice-Wonders-Series-John-Davis/dp/08...