They build and constantly maintain whole infrastructure, making repairs and modifications from time to time, they are numerous and very useful servants of Sauron, a cheap and strong labour force. The roads are really good for transport inside the Black Land and connecting with other lands (and there are horses in Mordor either stolen from Rohan or bought or plundered from other lands and bred in Mordor so some areas must be useful grassy plains with tussocks if they indeed have local population of horses, we know there was a cavalry forces in Minas Morgul as well as Haradrim cavalry and that of Easterling, though in whole it’s numbers are fewer than that of infantry), huge empire Sauron rules, lands conquered in many campaigns, tributary lands, allies and slaves he deceived and corrupted, peoples for whom he is a worshipped god-king. Tributes and spoils of war ,,wagon-trains of goods, fresh slaves” etc. are everflowing stream coming from East and South. Even more or less independent orcs of Misty Mountains pay tribute to Sauron (well at least those orcs who at various times took over and plundered Moria, they paid Sauron tribute in mithril though themselves feared to mine there due to presence of Balrog, other societies of orcs in this mountain range can be on their own, but Sauron also sends his servants among them to seize power among local orc tribes and clans from the independent chieftains and orc-kings). Orcs accumulate waelth through waylaying travellers, making raids for spoils and slaves and presumably they know and use currency, they simply like riches (Azog’s purse of money shows that they indeed know value of money) they might engage in commerce with other races or among themselves (also they simply barter and exchange loot) or renegades of therof (maybe they are the originator of ,,black markets” hehehe but surely Sauron wold know and control trade of stolen and smuggled goods hehehe).

Already mentioned many times were huge farmlands of region known as Nurn (around Sea/Lake of Nurnen) very fertile and manned by thousands of slaves producing food for armies and possibly for trade, mines too would allow for selling resources and gathering nice income :) (it is really a large area of Mordor if not the majority of it, but even ashen plains of Gorgoroth are useful, also region of Morgai has it’s local plant life), nobody thought about that?

Sauron is grandmaster of strategy and planning, like in chess he sets everything like pawns on board. He is clearly a logistic expert :), he has everything resources, manpower and means and whole empire of lands to make his vision of new order (hell every orc in Mordor has number and rank, clear chain of command, not only orcs but also men live in Mordor and they live in there quite well, not all of Mordor is complete desolation or desert either). I imagine that Mordor and even Gondor (in times of it’s imperial might and really huge territory stretching from Great Sea Belegaer in the west to Sea of Rhun in the east) works a bit like ancient Rome and we know that Imperium Romanum was highly successful and well organized in terms of both economy and military (of course there are numerous differences, for example Gondor never practiced slavery, like Mordor and real life Rome did). Also about Isengard,we know that region known as Wizard’s Vale was fertile farmland with slave worked fields like sothern Mordor, Saruman had also willingly working men as employers and he traded for supplies (he had spies, informers and connections with local populations as far as Bree-land and Shire’s Southfarthing, having shady dealings and businesses with them :) ). Saruman after beign given fortress of Isengard for his own had both money and resources for his future operations once he fell to dark side :).

If you want a fresh meat supply that eats food that orcs don’t then you need ruminants: cows, sheep, goats, deer, giraffe, …

The mass of low paid but rule-following employees would make Mordor an ideal location for a palantir-based call center and low-level support. Gondor kids would be flooded with very cheap “Forged in Mordor” iron toys.

Post-war there’d be a thriving business in battlefield tourism and reenactments. There’d be merch sales for things like Red Eye bumper stickers and ironic hipster t-shirts with a grinning Mouth of Sauron.

And the Uruks have a tradition of producing fine defensive linemen. They’d be sending GFL income home to their spawn-brothers back in Mordor.

Sauron only concentrated them into armies when it was time to march on Rohan and IsengardGondor (though there was a decent force in Osgiliath for quite a while?). Also, I can’t remember the if the texts gave any hard numbers for the size of those armies, but I wouldn’t imagine the one outside of IsengardGondor being much more than 70-100 thousand in size. Admittedly, that would be a logistical achievement of tremendous scale.

Rome could be fed from Egypt because all of the grain trade was via sailing ship (oars when becalmed or maneuvering into dock). As long as the boat moves faster than the crew eats the grain, no problemo — and wind sailors need fewer calories than an entire crew of an oared galley. Hit Italy, unload at a major (and dedicated) port, then barge via canals and rivers to the city. And that is just feeding the capital city — not the majority of Roman Italy!

If you have to go to muscle power (including animal), your maximum transport range is severely limited — eventually, your entire useful payload is used up feeding the oxen (or horses, or slaves). Figure two weeks, roughly. Two weeks isn’t very far.

Likewise, how long before you have hit full market saturation with your trade goods in the area you can reach? Sooner or later, someone like Elrond will say, “You know what? We have plenty of swords, and we can suck it up without cheap nails for a while… let’s starve the bastards out!”

“We’ll just forage, thus not eating the cargo!” That’s cool, if you’re in a fairly lush grazing area (American Prairies during westward settlement), and you’re not transporting huge numbers back and forth on the same path. Grazing also takes time — might cut your daily travel by as much as half… and from all appearances, Mordor was seriously lacking good grazing near the capitol.

If you’re running The Red Ball Express of Sauron, you’ll have eaten out the available grazing near the roads, fouled the ground near the roadways with manure (oh, yeah, road crews to shovel sh*t, gotta have those!), and pretty much been forced to carry your own fodder from about the third trip on.

“But wait! We’re talking about feeding the population on pigs, not grain!” Sorry, pigs gotta eat, too. And they eat about as much as a human would, pound for pound — their advantage is, in an area with surplus (but unappetizing to humans) food, pigs are great, because they can eat swill or scavenge stuff like acorns.

Pigs in an inherently food-deprived region (sociologists suspect that one reason pork is verboten to pre-industrial desert dwelling cultures, by and large — pigs compete for human food and potable water in an arid, food deprived region, to a FAR greater extent than, say, goats). (OTOH, in a temperate and green area like, say, pre-industrial Europe, pigs are great! Plenty of stuff they like to eat that people prefer not to. Likewise, they travel well, and the combination of forage and leftover swill means they are awesome food “on the hoof” for moving armies. Of course, if you’re on the move, the pigs won’t fatten up nearly as well, because they are burning calories walking, but life’s a series of trades…)

Can’t just ship pig carcasses — not only do you have to feed the animals moving the pork, but it will only last a limited time before even vultures start saying, “Ewww!” You can properly kill, butcher, and preserve the pork, but that severely limits how much pork you get for your 6 pence per sword…

So, if you’re feeding the orc armies on pork, you have to feed the pigs. If you have to feed the pigs, you’re back to square one.