You pandaren tried to bury your hate and your anger, but such power cannot be contained. It must be unleashed!
- Garrosh Hellscream to Taran Zhu
The more I think about it, the more I believe it. This was all going to happen, with or without the presence of the Horde or Alliance. In fact, the presence of those two warring forces may have ultimately saved Pandaria from complete destruction. When Garrosh Hellscream defeated Taran Zhu and hurled the Heart of Y'Shaarj into the waters of the vale, he mocked the Shado-Pan's leader first about the pandaren and their tendency to suppress violent emotion. It's an understandable tendency in a land where emotions like doubt, anger, fear, and hatred can give rise to the Sha, but it was a tendency mired in one crucial error - there was always one Sha who wasn't imprisoned when Emperor Shaohao freed himself of the burdens of the others. For over ten thousand years, Pandaria dwelled in isolation, believing itself special among all the places in the world, believing that it had nothing to gain and nothing to learn from the outside. And in its special exceptionalism, its beautiful but stagnant isolation, the people of Pandaria settled into an eternal and endless cycle that allowed nothing to change it.
But a thing that does not change is not alive.
It's painful to look upon the Vale of Eternal Blossoms after Garrosh's actions, to see the blasted, corrupted land where waters flowed freely, to see the destroyed and defiled beauty. Taran Zhu blamed all those who came from outside Pandaria, and he's not wrong - it is because, at long last the mists have parted and new peoples have entered Pandaria that the Vale was destroyed, just as it was because of the same outsiders and their foreign war that the Sha of Doubt erupted and the serpent pillar fell. Destruction had indeed followed in our wake.