Foreign policy: 5 key points
First, if you have the power to right wrongs, you have the duty to do so. The world, just like any other geography, needs a policeman. Ideally the UN would serve that function. It has not.
Second, the US has recently abdicated its responsibility, letting Russia take over Crimea, and Iran take over Iraq, letting ISIS take over half of Syria and Iraq and part of Libya.
Third, if you are unwilling to risk going to war, you will always lose at the bargaining table. Diplomacy does not work if you have no credibility.
Fourth, there is no easy answer to any specific conflict. Devil is in the details. Specifically, whether the lessons of Munich, Vietnam, or Iraq are most applicable depends.
Fifth, humility, skepticism, and empathy for those burdened with the responsibility of making tough decisions. Second guessing is easy.