Stratfor has an in-depth article asserting that "Americans are not important because of who they are, but because of where they live."
The American geography is an impressive one. The Greater Mississippi Basin together with the Intracoastal Waterway has more kilometers of navigable internal waterways than the rest of the world combined. The American Midwest is both overlaid by this waterway and is the world's largest contiguous piece of farmland. The U.S. Atlantic Coast possesses more major ports than the rest of the Western Hemisphere combined. Two vast oceans insulated the United States from Asian and European powers, deserts separate the United States from Mexico to the south, while lakes and forests separate the population centers in Canada from those in the United States. The United States has capital, food surpluses and physical insulation in excess of every other country in the world by an exceedingly large margin.
The most distinctive and important feature of North America is the river network in the middle third of the continent. While its components are larger in both volume and length than most of the world's rivers, this is not what sets the network apart. Very few of its tributaries begin at high elevations, making vast tracts of these rivers easily navigable. In the case of the Mississippi, the head of navigation -- just north of Minneapolis -- is 3,000 kilometers inland.
The network consists of six distinct river systems: the Missouri, Arkansas, Red, Ohio, Tennessee and, of course, the Mississippi. The unified nature of this system greatly enhances the region's usefulness and potential economic and political power. First, shipping goods via water is an order of magnitude cheaper than shipping them via land. The specific ratio varies greatly based on technological era and local topography, but in the petroleum age in the United States, the cost of transport via water is roughly 10 to 30 times cheaper than overland. This simple fact makes countries with robust maritime transport options extremely capital-rich when compared to countries limited to land-only options. This factor is the primary reason why the major economic powers of the past half-millennia have been Japan, Germany, France, the United Kingdom and the United States.