It works better abroad than here. "Boycott the United States" has a lot of resonance everywhere else in the world and is to some degree doable. It's harder to boycott the United States if you are in the United States. (I suppose you could live off imported foods from the deli section.)
On the other hand, organizers in the US could promote the boycott-the-US message outside the US, issue calls for it, support it, collect information and so on.
If someone asked me to boycott company X to oppose the war I would be skeptical, but if someone asked me for ten dollars to support an international boycott organizing drive I would give it and I might go out with a fund raising bucket for it.
LP