When you say unjustified war, meaning that the war broke out for no reason at all. Unfortunately, wars are started due to so many different reasons. Some of the reasons are clashing beliefs of two groups or nations, for the conquest and the act of showing one's power to another country, and others just for business. And just like most replies stated, it is very difficult, or even near impossible to stop a war because stopping it would mean changing the belief of people who are in it, and that is pretty much impossible, when someone fights for what he thinks is right, it is usually in the extremes which is very difficult to change.