Zerf could have stopped all this shit from happening if he had just asked for the dragon slayers help to take down Acnologia. Hell even ask Irene and God Serena to convince them. Then they wouldn't need a stupid war in the first place. Zerf wanted Fairy Heart hoping it would take down Acnologia it wouldn't have done nothing considering Acnologia is immune to magic. Yet dragon slayer magic combined killed him. All fairy sphere did was freeze his body in place. So that acnologia couldn't move.
I guess he assumed that even Dragon Slayers wouldn’t be any use against Acnologia. To be fair, he did live through a generation of Acnologia running rampant, so that belief might not have been totally unfounded. He could have at least tried, though.
God Serena could have used his position on the council to recruit the Slayers, if he hadn’t defected so spectacularly. Irene could’ve made an army of wizards with dragon slaying enchantments. Buffed the Slayers. All sorts of things! Instead we got a war we didn’t need (there was literally no reason for a war, my god…) and a timetravel plan that… well, Zeref could have walked through that door at any time if he hadn’t done the obligatory showdown with Natsu.
Zeref’s an idiot, is what I’m saying.