The Warsong Clan's position in Horde politics remains confusing at best, even now that Garrosh is up and being grumpy. Originally they were just Hellscream's orcs, fighting the night elves in Ashenvale because they want lumber. Now, they are all over the place, being Warsong guards and such. It's somewhat unclear, but I think originally, after Grom's death and the World Tree gets blown, the Warsong orcs just get ignored and go back to getting lumber.

Thrall never seems to make any sign of caring, but if he had in the beginning, they could have probably saved themselves from getting the night elves into the Alliance.

The tauren's standpoint with the Night Elves stil remains extremely unclear as to why they are both such buddies since the start, as their respective pasts are relatively mysterious. The tauren have probably existed since the Great Sundering and they must have interacted with the night elves or something. I assume the appearance of Light/An'she-following Tauren in Cataclysm might explain it more.