I don't understand the concept of war.

I apologize if I may say something either controversial or something really wrong here. This isn't related to any recent wars and/or news. I'm just really curious :)

I don't understand why we have wars. Why do we have to waste YEARS of human, societal, and technological development and advancements because leader A did something to leader B's country or leader A wants leader B's resources or territory.

I know before an actual war starts, governments and leaders often talk it out diplomatically but something escalates causing a declaration of war. Life isn't all rainbows and cupcakes sure but aren't there less destructive methods aside from wars like economic sanctions or diplomatic negotiations. Why does it seem like we always want to or rather, why does it eventually lead to war?

Call me a pacifist or whatever the term is but why war? It just feels so destructive and stupid to waste so much money, so much progress and development because two leaders don't agree with one another. The worst part here is that civilians and soldiers suffer more here than those that started the war.

Don't we fear that if a war DOES start and it ends, we'd pretty much go back to square one? We'd pretty much have to possibly reinvent or do everything from the start. No one benefits from a war but why do countries still do war?