Each country has its own requirements for foreign visitors who want to drive. Some, like Canada, recognize U.S. driver's licenses. Others require an IDP, and a few require separate documents. That's why AAA recommends bringing an IDP along with your U.S. driver's license to help avoid many potential hassles, especially if you're traveling in a country where English is not the primary language. Even if an IDP isn't required, you may encounter traffic police or other officials who can't read your U.S. license but can read one of the IDP's 10 other languages.
Not sure what the rules are where you'll be traveling? Ask the experts at your local AAA branch in person or over the phone.