I'm aware of anarchism's role in the Spanish Revolution, but I'm not sure what we can really say about that experience. It lasted a very short time, mostly due to factors outside of its control, but also because it was part of an unstable political front with the communists and other liberals. How much of that instability was due to anarchism itself? It's difficult to say.

Don't mean to sound anti-anarchism, because I understand the sentiment. Thanks for more examples. Also:

https://en.wikipedia.org/wiki/History_of_anarchism