House Cannith perfected modern, sentient warforged in 965 YK. The Treaty of Thronehold, which ended the Last War and required House Cannith to destroy the Creation Forges, was in 996 YK. All (legal) warforged were produced during this 31-year period. The combatants during this timeframe were:
- The Five Nations:
- Darguun was one of the most important fronts in the War, particularly between Breland and Cyre, and at any given time Breland controlled significant chunks of it. All that ended in 969 YK, though, when Haruuc staged his rebellion, so there were only four years in which there were both warforged and Darguun as an active battleground in the War.
- Cyre itself occupied the area now known as the Mournlands.
- As noted above, Darguun was originally a part of Cyre, and the site of a lot of fighting between Breland and Cyre until 969 YK.
- The Talenta Plains were considered part of Cyre at the outbreak of the war, though by 965 YK they had lost much of them to Karrnath. The actual border would go back-and-forth often during the War.
- Karrnath controlled whatever of Talenta they’d managed to take from Cyre, which varied considerably over the course of the War. By the time of the Mourning, that would have been all of the modern-day Talenta Plains—anything Cyran at that point became part of the Mournlands.
- Zilargo, which was formally allied with Breland
All Five Nations are known to have bought and used warforged, though not equally—Cyre used by-far the most, with Breland as a somewhat-distant second, and other nations a fair bit distant behind that. Of the Five Nations, Karrnath is known to have used the least, since their undead served much the same role and were vastly more efficient and accessible for them. Aundair’s military relied more on arcane might, and Thrane’s on zealots from the Church of the Silver Flame, so the warforged did not fit into those militaries as neatly, though of course they still had use. The Church of the Silver Flame was—and still is—somewhat uncomfortable with warforged, as it is not clear how the warforged do or don’t fit into their beliefs.
It’s unclear how much Zilargo was or wasn’t buying warforged, though as an independent nation actively participating in the War, it’s all-but-certain that they had a fair amount (unless they just relied on their alliance with Breland to protect Zilargo and forwent establishing their own warforged force, but this seems very unlikely and uncharacteristic for the gnomes—if nothing else, they love new toys almost as much as Cannith does).
As for the rest, the Demon Wastes,1 Droaam,2 Q’barra,3 and the Lhazaar Principalities4 were only nominally a part of Galifar and their respective Nations, and in any event no substantial combat took place on the corners of the continent. The Mror Holds,5 Q’barra,6 Valenar,7 the Eldeen Reaches8 each declared independence before 965 YK, in 914, 928, 956, and 958, respectively. These nations were no longer taking part in the Last War by the time warforged rolled around, and at the prices Cannith was charging for them, almost certainly did not buy any.
The Demon Wastes aren’t populated at all, not really. There are orcish warcamps, but these are all temporary dwellings for people who are really from other parts of the continent, mostly the Eldeen Reaches and Shadow Marches. They certainly did not have the funds for warforged. Aside from that, there’s only the Lords of Dust. If one of the Lords of Dust acquired any warforged—a terrifying thought—they certainly weren’t officially bought and paid for by anyone identifying themselves as being from the Demon Wastes.
Droaam was—and, officially, still is—part of Breland, but Breland’s control of the area was minimal even before the Daughters of Sora Kell forced King Boranel to evacuate any Brelish citizens and seal off the passes to Droaam in 987 YK. Droaam does not border any other participant in the Last War, so it is exceedingly unlikely that Breland had any warforged troops there at any point, save perhaps to assist in the evacuation, and it’s doubtful that House Cannith would sell to the Daughters of Sora Kell, not that there is any reason to think they’d want warforged.
Q’barra had no Galifaran settlements at all at the time.
It’s possible that a Lhazaar pirate lord might have bought a warforged, as a novelty and/or status symbol, but none of them could have afforded them in large numbers—many pirate lords are extremely wealthy for private individuals, but their wealth is not that of major nation–states—and even those struggled to afford warforged.
The Mror Holds basically never really submitted to Galifaran rule in any but the most superficial of ways. Outsiders were not, and still are not, generally allowed into the deep places where the real decisions are made for dwarven society. Both joining the Kingdom of Galifar in the first place and then later declaring independence from its sundered nations changed very little about the real workings of the Holds.
Ven ir’Kesslen led an expedition of dissatisfied Galifaran royalists to Q’barra to establish an independent kingdom that would supposedly hold true to the ideals of the Kingdom of Galifar, rather than the petty squabbling of the Five Nations. No one really cared, and the Q’barran settlements had no input in the War.
Valenar, of course, had been a part of Cyre, before the Valaes Tairn declared their independence. Fiercely proud of their own martial prowess, buying warforged would have been totally out of character for them; if they had been forced to admit defeat, they sooner would have just retreated back to Aerenal than they would buy warforged. And in reality, no one seriously challenged their claim—neither Cyre nor Karrnath could afford to do so at that point in the war, and no one else was nearby.
The Eldeen Reaches are focused, of course, on the natural world, and is run by druidic circles and agricultural communes. They declared independence specifically to remove themselves from a War they felt was not theirs to fight in. They could not possibly have had less interest in warforged.