Day of the Dragon was published between Warcraft II and III, so it uses outdated maps. I am not sure if it was in DotD or Behind the Dark Portal, but Gilneas was mentioned as kingdom which shouldn´t care about Alteraci inheritance, due to them being located far away from Alterac. But, as we can see from WoW, Ambermill (which belonged to Gilneas before building of their wall) was divided from Alteraci territory only by Dalaran and its surroundings. Stromgarde trying to annex eastern Alterac makes a lot of sense when looking at Warcraft maps, but not when we consider WoW maps, which are correct ones (and there was no continental shift, Warcraft maps have been retconned, so it always looked like that).
Also, those are all information from books, which are on lesser level than games. When book from 2001 mentions A, but information from game from 2004 suggests B, then game is right. Alterac really seems like landlocked nation, located in the mountains.
Gilneas is in a quite different situation here than Stromgarde is. Stromgarde is trying to annex Alterac: Gilneas was trying to put a puppet onto the throne of Alterac, which doesn't really require a shared border with Alterac. However, annexing and administering part of Alterac, if Alterac is seperated from Stromgarde by Lordaeron territory, is not a very viable option for Stromgarde if Lordaeron opposes it (and Lordaeron did oppose it). We're led to believe Thoras is a master strategist, so he should understand this.
I'm not sure what your second point is saying here. "WoW information contradicts this"-- but it doesn't? WoW tells us that Durnholde exists, and really nothing else about Eastern Hillsbrad. The human territory we'd see in between Alterac Mountains and the sea--Durnholde--was built after the Second War. We know that Lordaeron annexed parts of Alterac after the second war (Strahnbrad, which is seen in the first mission of the Human Campaign of WC3 as a Lordaeron aligned town), so it's not an unreasonable assumpion to assume that Durnholde was built on land also annexed on Alterac-- we know that it was built after the Second War, we know that that land fits perfectly with the idea of an 'Eastern Alterac' that Stromgarde wished to annex, and that land would fit perfectly for giving Alterac it's port and the possibility for a fleet. Besides that: wouldn't it make more sense for Terenas to build a fortress in occupied ruins of enemy territory, than to build a completely new fort in his own lands? It'd manage to serve a double purpose.
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