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So, as it turns out, on another site I'm debating a really hard-core pacifist. One of those 'don't lift a finger to protect others or yourself' people. She essentially sees all war as evil, regardless of result or motive. So, I'm wondering, can you help me prove her wrong? I'd especially like historical examples of times when pacifism/peaceful efforts failed and/or war achieved a positive result.

Please get rid of this post.

While it is hard to argue against pacifism for the individual, it is obvious that it'd fail on a societal scale.

Sure, your society might be a perfectly pacifistic and therefore violence-free one. But as soon as one of your neighbors decides not to play by that rules, your society will no longer exist (due to being overrun by non-pacifists).
That is certainly unfortunate, but that's the way it is.