Look at what GB did when they where teh greatest super power. They caused all sorts of problems. They started Isreal, South African Apartide, North Irish unrest, general poverty in africa, and several smaller problems in asia.
When GB was the worlds bully and where involved wiht EVERYTHING in the world they cause more problems than they solved.
IMO the US is starting to do the same thing, after WWII (possibly Korea) and the US changed its non-involvment policy, there have been more problems cause than solved by the US.
Isreal (again), Iraq, Cold War, Vietnam, Somalia, theres more that i cant think of at the moment. But if you look at the resemblance between GB and what the US is doing now, it makes you question if the US has the right idea or if they should just stay the hell out of world politics, save for when people like Hitler come around.