Hello!
There are several different reasons why we might need to worry about the problems of other countries.
First, we import goods from countries all over the world. If there are problems with other countries, it may limit what we can import and export to and from the country. If we are no longer able to receive any goods, it may have an impact on the U.S. if the people suddenly don't have a certain good/product available.
We also need to worry about the problems of other countries when it comes to partnering and working with other nations. If the other countries are working with enemy nations of the U.S., the United States will not be able to partner with them. The problems that other countries have could eventually spread to the U.S. if we are not aware of them and not careful about our decisions.
I hope this helps you! Have a lovely day!
- Mal