thats my whole point from the start. ( you are still missing it).
The agression needs a other catalyst ( cause/spark) for the war. Thats why i said. si 7 ( or sylvannas planted some evidence) to make it look like the alliance started the war. Or did some bad things.
Right now the story is from "peace" to mass murder war in 2 seconds flat.
A couple of quests /lore ingame that gives better motivation.