If diplomacy is damned effective, why do so many countries even bother with maintaining a military force at all?

The truth is that diplomacy simply does not work against an adversary that is determined to blow your ass up.

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"Why, it appears that we appointed all of our worst generals to command the armies and we appointed all of our best generals to edit the newspapers. I mean, I found by reading a newspaper that these editor generals saw all of the defects plainly from the start but didn't tell me until it was too late. I'm willing to yield my place to these best generals and I'll do my best for the cause by editing a newspaper." -- Gen. Robert E. Lee