Sauron's Armies

[Kuruharan]

I believe there was an army once with 250,000 soldiers - not sure but may have been Norman/Viking perhaps?

Not Norman or Viking, no. Their armies never were anything like that big.

In the age of armor and sword armies were small because of a few necessities. A) Populations were not large enough to support armies hundreds of thousands strong. B) An army that size could not be fed. It could not bring enough food along with it to feed itself over a campaign (even assuming that it would be able to gather that much food) and it could not live off the land for any amount of time before it would starve.