The logic here is straightforward: the more powerful a state is relative to its competitors, the less likely its survival will be at risk. No country in the Western Hemisphere, for example, would dare attack the United States, because it is so much stronger than any of its neighbors. This reasoning drives great powers to look for opportunities to move the balance of power in their favor, as well as to prevent other states from gaining power at their expense. The ultimate aim is to be the hegemon: that is, the only great power in the system.