I think the USA will still be a leading power in the world but not THE leading power. I suspect it will be overtaken by China - probably within twenty years.
Additionally, there is a new philosophy beginning to emerge - especially in the so-called 'advanced' nations, a burgeoning belief that we live on a Globe without boundaries and that no one nation, or even conglomeration of nations, can dominate and exploit the rest without there being terrible long-term ramifications.
Ease of worldwide travel, the Internet, widespread migration from the poor countries to the richer ones, will eventually cause those richer nations to think, "Let's make it worthwhile for people to stay in their own lands, not by force but by making them so desirable in which to live that they won't want to come - expect perhaps for a holiday." Let's treat them fairly.
The days of 'nationhood' are numbered. World citizenship, a world without passports and criteria as to who is worthy and who is not is gradually making itself felt. I won't see it in my lifetime, but I'm pretty sure it will be this way before the next millennium.