All they needed was a supply route. With the abdication of Warchief Thrall and the rise of the new Warchief, Garrosh Hellscream, suddenly the Alliance discovered what it meant to have a true orc at the helm of the Horde -- a merciless killer who held no particular love or wish for understanding and peace. Suddenly, the days of mild skirmishes were over, and the attacks in Ashenvale and Stonetalon had begun in earnest as the Horde moved from quietly settling the land and using its resources to taking it by force.
The night elves struggled to fight back, but the remote location, so far away from the human settlements of Northwatch Hold and Theramore, left only one route for the Theramore forces to take in order to get those supplies delivered. It was one that took them straight through the heart of Horde territory -- the harsh, expansive desert of The Barrens. And so the Alliance came up with a plan: A road was to be constructed. With a road, the Alliance could easily transport caravans and troops to defend those caravans and help their allies defend against the crippling attacks.
It was just a simple road.