Combat

It's true we've been in several unnecessary wars, but we haven't been in one or another since we were founded

And many wars are only unnecessary in hindsight, at the time the choice may not have been as clear

That's a pretty good point. I suppose. It makes me think of the George Santayana quote "Those who cannot remember the past are condemned to repeat it."

^ The Gulf War and the one on Terror, though...not to mention their nasty effects...