In general, intellectual property rights are territorial in nature, meaning that the protection afforded under U.S. laws does not expend beyond the boundaries of our country. Copyrights are no exception.
For a work to be protected outside of the country of origin, the home country must have a bilateral agreement with the country where the work is used. There are several international copyright treaties, the most important of which is the Berne Convention.
Under the Berne Convention, all member countries must afford copyright protection to authors who are nationals of any member country. This protection must last for at least the life of the author plus 50 years, and must be automatic without the need for the author to take any legal steps to preserve the copyright. The Berne Convention is signed by more 100 countries, offering copyright protection in most industrialized nations.
In addition, the GATT (General Agreement on Tariffs and Trade) treaty contains a number of provisions that address copyright protection in signatory countries. In combination, the Berne Copyright Convention and the GATT treaty allow U.S. authors to enforce their copyrights around the world, and also allow international authors to enforce their copyrights in the U.S.