When is War right?

Let me start by saying that I am not a proponent of war and I believe diplomacy is always the best policy when possible. So this post doesn't represent my views that War is the right cause of action all the time I just want to share my opinion.

Yesterday I was driving home from training and I saw a bunch of signs saying Stop War on Iran. At first I was like word? we started war on Iran already? and then I begun to wonder. When exactly is war right? I mean all and all the major of the wars that we've been in have been because of a major catastrophe that happens. I mean think about American Revolution, well yes it was a fight for our freedom but the last straws happened when British started terrorizing the American colonist. We got into World War I because of Germans sinking our ships. World War II started because of the infamous Pearl Harbour and the War against the Taliban started because of 9/11. So my question is do we want to wait until something bad happens to us first and then react. Yeah of course the war on Iraq was a mistake for many reasons. But I think the government wants to take a proactive approach to these types of issues. They don't want to wait for another disaster than have the backing of the country and even those people with the signs. I don't think we should sacrfice human life in that way. I think if you can find proof that countries or groups are trying to find ways to harm our way of life and strong proof that is, none of this I think they have Weapons of Mass Destruction crap. If there is concrete proof then maybe we should look into it. Instead of waiting for something to happen and then that's when you put those signs down and make War in Iran signs. Make up your minds buddy, you cannot have it both ways