Although the term is never defined specifically, the evidence provided tells us that, in Eberron, "fiends" is the generic term for demons, devils, and other evil outsiders that were spawned from Khyber at the dawn of the world (ECS, page 224). They seeped up from the cracks in the earth, from volcanoes and the deepest parts of the sea (p.158). They are capable of possession (p.100) and are led by outsiders more crafty than they are.
It can be inferred that, since the cosmology and planar structure of Eberron differs from the typical Great Wheel of D&D, the terms "demon" and "devil" aren't relevant to the setting. "Fiend" makes a nice generic.
I can’t find any suggestion that the giants had anything to do with the origin of the elves; the elves seem to predate the giants’ rise to power, actually existing during the Age of Demons, at which time the “lesser races” (i.e. not demon or dragon, apparently including at least the elves, giants, goblins, and orcs) simply tried to avoid getting killed in the war between demons and dragons.
After the couatls sacrificed themselves to end that Age, the giants were able to rise to power in Xen’drik using dragon-taught magic, ushering the Age of Giants.
The giant empire then enslaved elves, and thus “inadvertently” raised them up out of their primitive state, teaching them magic and the like. Towards the end of, or just after, the war with the quori, the elves revolted. The giants were going to put this down using the same cataclysmic magic they’d used against the quori, but the dragons came and crushed them, instead. An elven prophet/hero named Aeren, among other things, foresaw this end and signaled that the elves should flee Xen’drik before it happened.
Those elves named the island they fled to “Aeren’s Rest” or Aerenal, and referred to themselves as the Aereni. Aeren had sacrificed himself during the exodus, but not before figuring out how to do the whole undying thing, so he became the first undying councilor.
The drow, of course, stayed in Xen’drik. Simply based on the fact that all elves from Xen’drik are drow and no Aerenal elves are drow, it seems likely that the actual distinction between “elf” and “drow” happened after the exodus, probably during or immediately after during the dragonfire-purge.
However, Secrets of Xen’drik does have this:
According to one legend, the Sul’at giants created the drow by binding dark forces to normal elves
The Sul’at League was a series of fire giant city-states, founded by the first fire giant Adaxus, who got that way through some fiendish pact. Or so legend has it, anyway. This is the only mention I can find of giants manipulating an elven race. That said, it doesn’t seem to jive with the facts, which calls that legend into doubt. It seems unlikely that every single drow would choose to stay and every single elf would choose to leave.
The elven trance is different from sleep, and their “dreams” are different as well. I am still searching for information about whether or not these dreams are similar enough that they still go to Dal’Quor in spirit while they trance.
Unfortunately, I have so far looked through Eberron Campaign Setting, Secrets of Xen’drik, Secrets of Sarlona, Magic of Eberron, Races of Eberron, and Player’s Guide to Eberron, all without finding any reference to elven dreaming or lack thereof, much less whether or not the giants were responsible for it. I didn’t read those books cover-to-cover, but anything that sounded like it might even possibly have the reference, I checked. I’m running out of even remotely likely suspects.
Best Answer
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:
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.