If we do not continue these endless foriegn civil wars, be it 17 to twenty years at a stretch, the US would leave a vacuum to be filled by some other country to play policeman to the world with a better or worse agenda than our own. Who would do it? Russia, China?... So we slog on.

On the other hand we have already been economicly defeated by our own rich citizens who control our banks and Wall Street. As a result we have no capital to engage in war. (and that bears repeating)

If the world wants us to be the police then they will continue to prop up our treasury with loans. If not, the loans will dry up and so will we.

So we fight out of tradition and a fear of someone else doing it instead.