The United States controls alone, at the present time, the shared "spaces" of sea, sky and space. This mastery, which is made possible by its huge economic power, is the basis for its military hegemony. This allows it to project its capabilities throughout the world and prevents any adversary from doing likewise. It also guarantees a high degree of security to the air and sea ways - used by all states -which means that many countries consider that the hegemony of the US is also in their interests, particularly economic ones. But this domination, as global as it is, is not total. There are some areas in which it can be competed with, and the last ten years have shown that a lesser adversary in technical, economic and military terms can rival the U.S., either in street or mountain fighting, air defence below 15 000 feet, or with terrorism.