[Fortunately, when you live for 5000 (at the very least), you learn to keep an eye on the world. He didn't spend all time on the mountain... just most of the time. And the Greybeards could be persuaded to gather such information for them.]

I have told you it is a land of swaps, have I not? What land there is cannot be traversed easily, ships cannot fit through the rivers after a point... And they are beings of the water above all else. It is not unusual for some of their homes to be beneath its surface. Any who would attempt to follow them would learn quickly that to fight them in their home territory- to fight creatures of sharp teeth and claw and who have spent their whole lives with water- would be a foolish decision.

As far as I had heard, none yet had ever been able to make it to their capital city in the heart of Blackmarsh. There has simply never been a way for those not of their kind.

And besides... [Paarthurnax gives a shake of his head.] The other races view them as less than. They once took them from slaves- especially the Dunmer of Morrowind. Even in Windhelm of Skyrim, the dockworkers there were treated poorly I had heard. So it is not surprising that that they distrust the other lands.

Such foolishness... After the crisis of Oblivion, one would think they would have received more respect.