How do we decide who's deserving of death in wars and who isn't? — Dilemma

Hi! Um firstly if I offend anyone then I'm sorry, these are my personal thoughts on war. I'd appreciate it if anyone listens to this. Also, it "might" be that I have a wrong take on this cause my prefrontal cortex isn't fully developed yet? (16). Idk if this is the correct place to post it but I js wanted to hear what my peers had to say on this. Anyways, today we had this mock drill in our school. There were traumatising sirens being played in the bg and believe me, it gave me chills. Literal goosebumps. If it were to be continued for an extended period I'd have cried. I just couldn't stop thinking about those children who have to actually face this. Those few moments of the drill made me hate and feel disgusted with wars even MORE. I never understood the concept of war. Idc if my country's involved even on the defence side. How do we actually justify killing children who don't even know politics. Or the innocent civilians who were just trying to live their lives. Is there no value for even a singular human life? And forget singular, the numbers are huge as we see how many civilians get killed in the name of "necessary evil". I might be called an anti-national for saying all this but honestly, I could never wrap it around my head that how humanity became so desensitised that blood and screams became patriotic and a sign of nationalism. I'll say this again, I feel the same for my own country, or any rebel country, or literally any part of the world man! Idc what race or culture you belong to, your lives matter! I get it, even if they (general term) are the one's who killed our soldiers, how can we (again, general) literally wipe out cities in the name of revenge? "Or vice-versa". That's literally slaughter disguised in the name of nationalism! Where's the empathy? Dead? I'm not targetting current state of the stuffs happening around the borders, I'm speaking all this in general terms. And anyone reading this is free to correct me/give their opinions. How do we actually justify war? How do we justify the screams of children, moms, innocent people, who all had nothing to do with politics? And if I'm wrong, how do I even make myself accept this shit. The idea of war disgusts me to the core I just don't understand why it even exists as a thing. If the reason for all of this is "necessary evil", then I'll like to end this by asking the question again: How do we decide who's deserving of death in wars and who isn't?

Thank you for reading this.