US Trademarks and other countries, like the UK

I understand trademarks are registered within a country, like the US for instance. Is a trademark then just valid in the registered country, or is there international agreements that trademarks in one country are protested from use in other countries (that have agreed via treaty or whatever).

I ask because I just found a UK website using the same name to sell basically the same product that the company I work for sells in the US. I kicked the issue upstairs, and I’m sure the lawyers will take care of it if there’s a problem, but I’ll probably never hear the outcome.

Copyright and intellectual property are handled a bit differently in the U.S. as compared to most other countries, however, for international purposes, the Berne Convention, is what regulates these things. I’m too lazy to search it for you, and IANAL.
I think the protection for TM is weaker than for copyrights and certainly for patents.

A company name can be trademarked in one country; if you use the name in another, you need to have it trademarked there, too. This allows a company in country B to use the name used by another country in country A.

In the US, for instance, the General Electric Company used to have to put on their material that they had no connection with the General Electric Company of the UK. (The British General Electric company eventually changed their name to Marconi in 1999, and the US company uses GE as its name.)