Plot against America...when should America go to war?

According to fivethirtyeight.com today, in May of 1940, 62% of Americans in a national poll said the US should stay out of supporting the allies in the conflict in Europe, even if Hitler was about to be victorious. What if Roosevelt was not reelected?

Zanzibar Chest referred to the value of one American to the number of Israelis and Africans. What about Bosnia, Somalia, Darfur...Syria? 

Should the decision be based on national security, national interests, war crimes, genocide?

Is there ever a good time to use force? Now that we are cutting back on international aid and diplomacy (state department). What is next?

I haven't quite finished the current book, but it does not look good for the alternative universe.