ish… Harry was prophecied to defeat Voldemort so he was the immediate target but Voldemort and the death eaters had nearly conquered the wizarding world before Voldemort attacked Harry the first time and their ultimate goal was to take over so it was fight the death eaters with the guy who was destined to stop them now or fight the death eaters without him later.
Voldemort and his death eaters were after Harry, not the school.
It was the school going to war for him, not the other way around.
ish… Harry was prophecied to defeat Voldemort so he was the immediate target but Voldemort and the death eaters had nearly conquered the wizarding world before Voldemort attacked Harry the first time and their ultimate goal was to take over so it was fight the death eaters with the guy who was destined to stop them now or fight the death eaters without him later.