A) It was an attack on an abandoned city.. Forsaken were forced out. We went there to kill Demons and rebel undead, not the Horde.
B)Horde terrirtory for the last 5 years but human territory for the 100+ years before that.
The Alliance didn't start any war. Get your facts straight. Lore says Undercity was not a declaration of war... YOU say it was.
I'm sorry but I'll have to go with the lore on this one...