Goblin levelling experience, near the end.
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It very much IS a declaration of war, don't be biased. If you ever did the battle for the Undercity event, you will remember that Varian was going to attack on the spot, but Jaina teleported the entire Alliance army (Varian included) away.
And you also have the gunship battle in ICC, meaning that there were already armed clashes between Alliance and Horde by then. Wrathgate happens canonically after Ulduar but before ICC.