http://www.catholiceducation.org/en/controversy/politics-and-the-church/the-just-war.html
Cliff Notes
War declared by acknowledged leader (prince);
Just cause; and,
Good to be accomplished or evil to be overcome.
Bingo!
With ISIS, unlike for a nebulous Islam, there’s a leader or set of leaders (the prince) and the named movement. It’s cruising for a crushing. Why it didn’t get one years ago is a marvel to me. Are we that paralyzed at this cult?
I’m not a Roman Catholic, but this particular systematization seems to make biblical sense. Christians don’t fight “as beating the air.”