I am just baffled by the Alliance fighting the Horde again, how do you defend it?

[Deleted]

Theramore deserved it. Their soldiers attacked first, razed Taurajo, and even had incursions into Durotar itself. Can you imagine if the Horde had boots on the ground in Eversong? Theramore was a belligerent military target, and the Alliance's biggest naval port in Kalimdor. By staging a feint upon Theramore, Garrosh both allowed civilians ample time to evacuate, and (brilliantly) defenders to rally - including the goddamned Kirin Tor, who showed their true colours just in time to get nuked (wew!). It was a strategic masterstroke, and the Horde still benefits from what Garrosh did.

Very glad to see Teldrassil ablaze. Losing Undercity is a bitter price to pay, but I have full faith that the Forsaken will be able to regroup in the Ghostlands and make holding Lordaeron more trouble than it's worth.

[Lelkowski]

Garrosh both allowed civilians ample time to evacuate

Well he allowed them to leave, then captured them and used as shooting practice.
Veeery honorable

[Zulkhan]

and the Horde still benefits from what Garrosh did

Doubtful at best. The Alliance recaptured Northwatch Hold and likely held control of the nuked zone, obviously planning to build a garrison replacing Theramore.

Of course, that could not be the case in the new BfA scenario, where the Horde is taking almost unquestioned control of Kalimdor.