I was reading through some of the earlier stuff that I was writing about the initial Celtic migration specifically and how I came up with a reasonable estimate that they would have a population of roughly 37 million, all the steppe-taiga-tundra could easily contain, within 100 years, if they had a conservative 120,000 original settlers. That happened and the tribes set to fighting amongst themselves a bit and looking for new lands to settle. The Sidhe empire to the south was promising territory, but they were epic sorcerers, even compared to the raw power of the Druids.
It was the Sidhe warriors that got itchy about Human incursions into their "forbidden zones" that started the war that brought their empire down. The tribes of the eastern steppes were attacked and culled like an over population of deer, or killed by these troops with the mercy they'd have shown a band of Goblins, their villages were burned and their people were slaughtered, this was around 150 AD. By 170 AD or 230 years after the migration, (What are we going to use as an abbreviation for the Garnian calender dates?) Gwaryn is declared High-King of all the tribes of man and leads an invasion force into the Sidhe empire. The Celts own potent magic, use of both chariots and cavalry, as well as iron weapons and their great numbers*. The Sidhe empire was swept before their tide of destruction, but it was vast enough that it took time to do, the campaign lasted for more than twenty years, and in the end, the southern 1/3rd of their empire was not as totally devastated as the northern 2/3rds. The campaign took on a less genocidal tone over time too, it was discovered that the Sidhe became weak and could not do magic if you put an iron collar on them, so many were enslaved.
Now the Romans, if the Celts were brought to Garnia by the forces of Darkness because they loved to fight, took heads as trophies, and practiced human sacrifice. I suppose when the Celts started turning all namby-pamby good on the Sidhe plane, because it emanates Good, they must have figured the people who scared the hell out of the Celts were a good bet for creating a more Evil empire in their place. They oppressed their women more, they kept slaves on a grand scale and had regular mass human sacrifice as entertainment for the masses. Plus they were militarily unstoppable, at least by the Celt and everyone else they'd met in the Mediterranean region. With the Sidhe out of the way, only the Dwarves really had to go, and they were already under serious pressure, so they took advantage and brought en masse the entire population that would have died and replaced them with simulacra, provided them with an intelligent and strong slave race that already spoke and read Latin and Greek, the Apes, put them in a place that was exactly like their home, down to the olive trees and vineyards, with pre-prepared housing and other needs taken from Earth. It was a huge undertaking, probably draining the power of several major Evil players for decades, perhaps centuries. I do need to figure out rough population estimates for this entire group of people that was supposed to have died, so I can expand their population over time and build their empire, they won't be taking Goblin Aegyptus overnight.
Now we still have to figure out when Earth's Mana battery dries up, how many times can the Dwarves or the Elves use gates to and from Earth, I assume it uses Earth's energy to open the portal and send them through from the Earth side to Garnia, and Garnia's energy to open to Earth. Garnia has energy to spare, it regenerates, Earth doesn't. So maybe the Mongols, or the Aztecs are good examples of cultures on Earth that Evil says"Finally, somebody we can really work with" and drags their asses through, but I am thinking the Byzantine Greeks might have been a rescue, or a spell someone figured out from some dusty old tome. The Iroquois could go either way honestly. The pre-Muslim Arabs and the Hindus? The Kung San? The Han Chinese, the Japanese? The Romany, Kushites and Basques? Obviously the Neanderthals were a Sidhe rescue program. The Saxons got here via forces of Evil because they were invading Britain, and actively at war with the Celts; it seemed like a no-brainer to the bad guys, it just didn't work out as planned.
This also makes a big difference because the Celts control and understand how to use a Sidhe portal to Earth, and they taught their compatriot Druids on earth how to use them too; this is essential for the multiple crossings plan. So I need some input on when the last Celts can freely leave Earth for Garnia, what makes sense? Ancient times? Pre-Christian times? Medieval Celts? Renaissance/Elizabethan Period? Early modern, runaway Jacobites could be fun, eh? 19th Century and the Potato Famine (1845-1852 in Ireland killed roughly 1million people and caused a further roughly 1 million to emigrate, about 25% of the population; the same famine struck the Scottish Highlands and Islands between 1846-1857, it's called the Highland Potato Famine there, and, while the death toll was lower, 1.7 million people were forced to emigrate** and many others suffered from severe malnutrition due to the meager rations the British government allowed them (24 oz grain/man/day 12/woman/day 8/child/day). This mass death and/or migration destroyed what was left of Gaelic culture, the English speaking areas of these countries were unaffected or taken care of by the government.
Yes, I understand that both Scotland and Ireland have Gaelic speaking regions, but there are damned few monoglot Gaelic speakers in the world anymore. Same goes for Wales, which has a thriving Welsh language, they successfully tied their national tongue to their quest to be recognized as a separate people from the English, but they all still speak English too. Manx is dead, although they're trying to revive it. Breton is on it's way out, the French have been trying to kill it with all the vigor that the English have been trying to kill their Celtic languages for just about as long, centuries. The last Cornish speaker died in the 1700's if I recall correctly. The sad fact of the matter is I think there are more people speaking Klingon fluently that there are any form of Gaelic.
*Roughly 10% of all Celts were warrior aristocrats, perhaps a further third had at least some training at arms and were fit for battle at any given time, the initial invasion force would have had 3.7 million professional full-time warriors and another 11.1 million lower born spearmen/slinger types. Plus the Druid-Priests, Wizards and Bards, maybe 1/2 a million or more of them.
**Including, in all likelihood, my great-great grandparents.