There are so many of these! Some examples:
- Climate change. This is one that the US and other countries have to deal with. They have to decide whether they are going to take steps to try to stop this problem even though those steps will be economically painful.
- European debt crisis. This is more of a European issue, but it affects the US as well. The countries in the Euro zone have to decide how they are going (or if they are going to) help countries in that zone which have too much debt. Greece's troubles are the greatest example of this problem and they might spread to other countries such as Spain, Ireland, and even Italy.
- Economic crisis. The US economy is still not improving very quickly at all. We will have to find a way to deal with that and that way is going to have to be able to get through Congress. That is very hard to do given how stubborn the Democrats and Republicans are being on this issue.
- How to deal with the "Arab Spring." We don't know what is going to happen with the Arab countries that have had revolutions and with those that are still trying to create change (like Syria and Bahrain). The US and the world will have to decide how to react to newly democratic countries that might end up having elected governments that we don't like.
These are just a few of the problems facing the world.