Admittedly, america doesn't have the best government, and some of it's decisions have been fairly stupid. And a handful despicable. But theirs no way it would invade the rest of the world.
For the sake of argument, lets assume the government is actually evil. They still can't fight the rest of the world. If they attacked Europe they would lose most of their allies and get into a fight with Russia, whose nukes can hit America. If it went after Russia straight away, China would step in to prevent America from continuing its encirclement. China, having intercontinental nuclear missiles and an industrial force America would struggle to contend with, would be a daunting enough opponent alone, but with Russia the odds are certainly in its favor. The middle east isn't really an option either. America has admitted to planing to attack Iran, but both China and Russia have said they would come to Iran's aid.
If america was as evil as you make them out to be, they wouldn't be dumb enough to fight the rest of the world. Even if they win American infrastructure would be wrecked and it couldn't hold onto its new territory.
>>1 Also Obama is not some sort of evil political mastermind. Americas habit of screwing over the rest of the world goes way back.