If another HItler comes along and says he wants to kill all Christians/muslims/jews/atheists/whatever then I'd support a war to defeat him.
I support war against ISIS too (although I'm not sure we'll win unfortunately ), since they want to take over the entire world. I don't mind having Sharia law in places if the populations there genuinely want it and vote for it peacefully. Going round the world killing people isn't the way to do it.
Unfortunately I think this is true. Chimpanzees, gorillas, etc. go to war too. Obviously they don't have guns and planes (their brains aren't as big as ours), but they do go and kill rival populations for resources or to remove competition, which is essentially what war is in our species...
Generally the act of war is necessary, but I do think we can be smarter. Not the best example but a lot of members here retaliate to terrorism by saying we should "bomb them all" without regard for the civilians, and even when you mention them, it's like they don't care.
We should be able to protect ourselves from terrorist groups as well as our rights, views and civilised society, without 'dropping bombs' on millions of people. You'd think we didn't have history classes and remembrance days for the world wars. People should be wise enough to know better and think of better solutions to the problem, much like dropping bombs on oil, and cutting the source of money that generates these groups. See, not hard is it. We seem to be doomed regardless but with the younger generation obsessing over 1D and caring more about likes, shares and selfies, I do wonder where the children bettering our world are.
), since they want to take over the entire world. 
I don't mind having Sharia law in places if the populations there genuinely want it and vote for it peacefully. Going round the world killing people isn't the way to do it.