There are international advertising agencies, however I'm not sure how you have started an "advertising agency" without knowing this. You need to do much more research. No one will take you seriously if you don't know something so basic about your industry.

Update: You can be based in the US and work for clients anywhere in the world.

International Advertising Agencies: BBDO Worldwide, Ogilvy & Mather, Saatchi & Saatchi, Leo Burnett...

Hello. I've recently started a local advertising agency. So far it is going really well. I've got quite a few clients and campaigns lined up. The local stuff is going very well. What i'm wondering is that, how can my agency become / do international business? How does an ad agency become international company, if that makes sense. Anyway please try to help with everything you might come up with. Thank you.