We fought in Vietnam to stop the "domino effect" of communism, but when the communists took over, the world didn't come to an end. We "saved" Kuwait from an evil dictator, but it's still run by a family dynasty that has no interest in liberty for the people. We waged war on Afghanistan to capture Osama bin Laden. Oddly, rights violations are still rampant and Afghani opium production has soared since the invasion. And then, of course, we have all the "good" done in Iraq.
This foreign policy of aggression and intervention, which we have seen grow in preeminence over the last century, just doesn't work.