A federal trademark registration with the United States Patent & Trademark Office(USPTO) is limited to protection within the United States. Outside of the country, similar marks are not automatically preempted without an additional filing (and even if they are, may be burdensome to enforce). You might be surprised to stumble across, for example, an Applebee’s restaurant near Shakespeare’s Globe Theater in London or an Old Navycafé not far from Paris’s Luxembourg Gardens.
However, registering your trademark internationally is not as burdensome as it may seem. The Protocol Relating to the Madrid Agreement Concerning the International Registration of Marks (Madrid Protocol) is an international treaty that allows a trademark owner to seek registration from any of the 96 parties with a single application. Instead of requiring individual applications in the language of each country where an applicant desires protection, the Madrid Protocol allows the applicant to file a single international registration through the United States Patent and Trademark Office. An international application may be filed electronically using the Trademark Electronic Application System for International Applications.
While every applicant may not need international protection, it may be wise to consider international registration if you anticipate using your mark overseas or know of potentially infringing marks. More information on the Madrid Protocol and international applications is available from the USPTO.