Some things never change historically/culturally. A "city" or a "nation" can exist where an administration has the ability to provide services in exchange for fealty. The chief service first sought by a population tends to be common defense, which allows everyone to live their quotidien lives in peace. And the more ready the natural defense, the more likely a nation can be created and preserved.

The best and most obvious example of this throughout history is of course islands. The vast majority of islands today are the homes of a single nation (yes, there are notable exceptions, such as Haiti/Dominican Republic ("Hispaniola") and Cyprus). Islands have an often formidable natural boundary which makes defense a reasonably easy task. Being situated between large rivers, or mountain ranges is another example.

Beyond the role of defense, internal services such as health, education, housing, commerce, etc., tend to be facilitated when a nation shares a common climate, via longitude, elevation, proximity, etc., so here again geography can play a major role. A nation like Chile is a great example of the difficulties faced in adminstration of a nation situated in a relatively finite space with spectacular variants in geography. Thus the geographic features within a nation are counter-productive to nation building, and problems with administration ensue. A classic recent example is the Soviet Union, for which administration ultimately produced bankruptcy. Likewise, we can witness within several hundred years the difficulties of administration of larger nations within Europe during the past 1500 years, such as France and Germany, whose mutual border remains somewhat murky, while internal geographic features tend to make provision of services far more expensive than in a smaller nation such as Luxembourg or Belgium.