Tomatoes come from Cyrodiil, which the Nords need to make horker meat taste good. /thread
Really, though, Cyrodiil offers quite a few benefits. A stable, continent-wide currency is the biggest benefit to commerce imaginable. That coupled with safe trade routes by land and sea (thanks to the legions, who also do police work) means huge boons to investment and the steady movement of food and other resources. The sharing of information and techniques made possible by a united Mages Guild was an incredible advantage as well. That's why levitation and teleportation were so widespread once upon a time. At peak unity, it was common for mages to move through physical objects like fences and even brick walls.
Skyrim is the reason Cyrodiil achieved and maintained military dominance in all three of its empires. The rows and rows of fresh-faced Nordic soldiers brought every other province into line, excepting the Altmer in Tiber's time, and the Argonians, who don't really count. Without Skyrim, the logistics of taking control of and holding on to High Rock would have been a nightmare. Without Skyrim, Vivec wouldn't have felt compelled to make a deal, which means the Dominion wouldn't have fallen apart.
So Cyrodiil might have taken over Elsweyr. But could they have without Wulfharth?
I'm not saying Cyrodiil wasn't a very powerful thing on its own. But their population probably doubles when they can recruit from Skyrim (and therefore from High Rock). Their economic, academic, magic, social and military organization is what makes made Tamriel work, but they wouldn't have been able to implement that system without the Nords.