What word or phrase represents this notion?

It is a traditional word or phrase which when used in the context of politics means that a territory or a nation, is capable of sustaining itself and flourishing by virtue of some inherent natural advantage. It is generally used to denote the geopolitical aspect of it, like a nation with lots of fertile land can obviously support more cities and a higher population. Or that a coastal city can trade and make money, and support itself in the process. Eg. The Mediterranean coast forms a ___________, which enabled multiple sovereign power centers to exist historically from Anatolia to Carthage. The western coast of India has for millennia been a ___________, which led to a differential economic development vis-a-vis the Gangetic plains.