Earlier quoted context omitted.
The future is scary if any sole country leads the world. Only cooperation and shared responsibility creates a viable future for humanity.
The present is already scary. The US have led the work without cooperation for quite a long time (remember the 2003 invasion of Iraq?).
This isn't quite on point, but all the collective guilt being slung about in these comments is problematic. I notice you use British collective plural -- "The US have". I don't know whether this is because you imagine the states collectively leading the world or the population of the states, but it suggests you assign collective blame.