Not all students of international relations would agree on the effects of being the sole superpower in a unipolar system. Some say that such a system is more stable than bipolar or multipolar systesms while others think htat it is less stable. However, there are some effects that are widely agreed upon.
The most important vulnerability faced by a sole superpower is the fact that every country that is dissatisfied with the status quo will “gun for” that superpower. When there is only one power, there is only one country on whom to place the blame for the world’s problems. We can see this very clearly in the problems that the US has faced since the end of the Cold War. The US, as the only superpower, is (for example) the obvious target for Muslim radicals who are dissatisfied with the state of the world. This is the biggest vulnerability that goes with being the only superpower in the world.