The United States' strength as a superpower rests on several pillars, including its geography, technological prowess, culture of innovation, financial and economic flexibility, relative political cohesiveness and military dominance. While any single pillar might weaken at one time, collectively, they give the United States a well-rounded foundation and lend it far more flexibility in dealing with its problems than any other nation. At the heart of U.S. power is its geography and the strategic depth that this geography provides . The nation's vast internal infrastructure is buoyed by a robust national highway system, as well as the globe's largest rail system and longest internal waterway network. Moreover, the United States is self-sufficient in almost all major industrial and agricultural commodities, with the exception of petroleum. Even then, it is the world's largest petroleum producer .