I didn't dig nor share Blizzard idea that Horde and Alliance need only a spark to start the war.
Time of racial war ended with WC3 ending, then it was ended once again in MoP showing the ugly face of xenophobia and "no winner" situation.
I thought sane creatures will learn their mistakes and take the peace gladly. Iron Horde once again show how the war is bad.
And on the Broken Shore, the Horde left Alliance alone after their leader was heavily wounded. They had a legit excuse, but they still left Alliance alone. Seeing the orcs and taurens as people of Honor, i bet Baine and Saurfang and their people had some little burden on them after doing this.
I mainly speaking about the Horde, cause it seems they were the first who hit Alliance once again, burning down the Teldrassil.
Dont Blizzard see that given all things i described above most of their main Horde characters won't start the war? Neither Baine, neither Saurfang (dont forget Eitrigg), nor Lor'themar. But it seems they gladly rush in it, like nothing happened before.
I dont know details, of course. But for now it seems that Blizzard simply butcher their story and their characters with this all out Horde vs Alliance war. It looks really noticeable because Blizzard tried too hard to tell us that Horde and Alliance are bloody enemies. They dont explain well WHY.
I believe with good story writing none of Horde leaders would follow Sylvanas (who, again, seems to be the only leader who really seeks vendetta) at worst. They would imprison her or kill at best to prevent of what happened in MoP, previous World Wars and following events of WoD.
If we will took into consideration that it was Alliance who started the war first, then the things would look even worse. None of Alliance leaders except Greymane has the really legit reasons to start the war given all previous events and the fact that its uhm... the war.