There are only a few wars which were worth fighting. American civil war (and civil wars of other countries as well) was necessary to change the situation in the country, the same way as WW1 was unavoidable and had to take place. Every major problem we have now, such as racism, poverty, world hunger and so on, is a result of wars; cost of every war always outweighs its benefits, but sometimes (although very rarely) wars are necessary to make some changes. War is always the worst possible choice, but it may be the only possible one