Anarchist checking in, so, y'know, bias and all that. But I'd say it's just as impossible to have anarchism in one country. Bearing in mind, I'm an anarcho-communist, and not terribly familiar things like mutualism, so that may be different. I tend to view, as do (to my knowledge) most ancoms, communism and anarchism as synonyms. The difference is how we get to the end point, not the end point itself. A stateless, classless, moneyless society. We've had the Spanish anarchists, and some examples of societies like Madagascar, where there are villages and region that function in an anarchistic way, but True Anarchism™ couldn't function in a single country/region. It needs to be international in it's scope for all the same reasons communism needs to be international in it's scope. Anarchist political methods can function at a smaller scale, but we can't have a fully anarchist society until it's global.

Which all just means that I'm an anarchist because I prefer the methods to achieving the shared goal, not because I disagree on the goal itself, if that makes sense.