Vedic era Indians - I am bringing them in circa 750 BC Earth time and they live at the southern end of the Tirnakaur peninsula, I am thinking one small, forgotten city that was destroyed by disaster, I think a great flood, 5,000 people. This makes them Hindu with all of the Vedas and they speak Sanskrit and work iron. Time compression means they've been here for 920 years or 46 generations at campaign present. That's longer than the Celts, but they start in a crappier area, those mountains are infested with Goblinoids and worse, then there's a vast expanse of forest to cross to get to the really good lands.
Pagan Arabs - They could really be from anytime before Muhammad, but I am going to try and keep a more ancient focus here and say they are from the semi-Mythical kingdom of Sheba; which is mentioned several times in the Bible and was probably in modern Yemen. They were traders and controlled the Red Sea trade route so coastal shipping is not beyond them, they were conquered by their Arab neighbors to the north in the 2nd century BC and their capital city was destroyed. They made a comeback eventually, but I am grabbing them from their powerful classical period, when they straddled the Red Sea as a kingdom. So, 300 BC, random natural disaster, say sandstorm of enormous proportions destroys major Sheban settlement of say 8,000 people. They end up on the same end of the Tirnakaur peninsula as the Vedic Indians, who welcome them as they are being hard pressed by an invasion of Goblins, Ogres, Giants and Trolls when they arrive with their slightly superior technology. They've been here for 770 years or 38 generations, also longer than the Celts. Their culture and language became slightly dominant over the Vedic Indians, but they mostly are pretty cool with each other.
Muslim Arabs - These guys can come from anytime after Muhammad, but I want them to be not right after his revelation or lifetime. I want them to have Damascus steel and Scimitars, so I have to wait until both of those are invented. I looked it up and it's later than I thought when I talked to Darryl about it earlier. Damascus Steel isn't a problem, it dates to the 3rd century BC, but Arabs didn't START using Scimitars until after the Mongol invasion and conquest of Baghdad. Call it a century or so later for them to be in common usage and we're looking at the mid-14th century. I am cool with that, we have some fairly late arrivals yet to come, and it explains their superior sailing technology. So 1350 a hardy group of Arabs end up over here, that's 220 years, or 11 generations, since they arrived and formed their "Maritime Emirates/Pirate Isles" and began wondering which direction was Mecca I guess. Give them an initial population of 5000 people or so.
Iroquois - Their confederacy wasn't even formed until sometime after 1450 AD, possibly as late as 1600, although the proto-Iroquois peoples were living in the Finger Lakes region as early as 1000 AD. I am acting under the assumption that we want real Iroquois and not their ancestral group, so I will pick a spot in the mid-range 1525, meaning they've been here for 162 years, or 8 generations. I will be nice though and move them into the forests of Tirnakaur instead of the Swamp that the Muslim Arabs live in; otherwise I think a stone age people are going to be slaves, even as bad-ass a stone age people as the Iroquois. The Celts in Tirnakaur have too much else to worry about to try too hard to make this new band of Humans their property. Which tribe of Iroquois do we want to bring? Should I just roll a D6? Or a D10 and divide by 2 because technically the Tuscarora weren't part of the league until 1722. We can't have them all. I rolled Mohawk, which is the result I think most people would have wanted anyway. Their relative low population density means I can't see them losing more than about a 1000 people without it being really noteworthy, and that's pushing it.
San - Apparently these guys, also known as Bushmen, have been in South Africa for something like 15,000 years. I am going to grab some from about the time the Zulus start to rise up and kick all of their asses into the Kalihari desert, these guys are serious stone age hunter-gatherers. They store water in Ostrich Egg shells and eat caterpillers and grasshoppers, along with anything else they can forage up. I am doing them the "favor" of moving them to the desert west of Wodanslund, otherwise they'd easily end up as a slave caste to the Muslim Arabs too. Now the Zulus really start to rise under Shaka, pre-Shaka they were just another clan of Bantu speakers in southern Africa, they mostly got kicked around by the other Bantu speakers and lived in crappy land that they forced some of the San out of. Shaka comes to power in 1816, Zulu ancestors had been in the neighborhood since about 1000 AD. So I am bring my San over in 1000 AD, they don't live in villages, just mobile bands, so this group of mobile bands, say 2000 people, just walk directly to Garnia World, how? Who knows, ancient San magic? Sidhe felt bad for them? Anyway, they have been here for 337.3 years, or roughly 17 generations.
The Roma - commonly known as Gypsies, they don't even come into existence until the middle ages, so we have to wait for that anyway. I am bring them in from 15th century France, they've got all the traits associated with Gypsies at this point (fortune telling, bright wagons & metal working) and they'll be happy to get away from the increasing prejudice. So 1450 AD, meaning they've been here for 187.3 years, or about 9 generations. We'll bring 1500 or so of them.
Lastly, the Aztecs - the entered the valley of Mexico fairly late, they were relative newcomers when Cortez came and kicked their asses. They showed up and started kicking ass around the 1300's AD, so we need to grab some before they all get infected with various White Man diseases by the Spaniards, before 1519. Let's pick a spot in the middle and say they were supposed to be wiped out by a volcanic eruption, but the Unseelie Court really loved their heart-ripping-out mass Human sacrificial style, a small Aztec city of, say, 12,000 people are transported to their new home, buildings and all, right near the coast so there's fishing too. They formed the Empire of Xochitli (which means "Flowers" in Nahuatl, the Aztec language). They've been here since 1425 AD, so that's 195 Garnian years, or about 10 generations.
Are we good now? Or do I have to add an addenda for initial populations for all of the ethnic groups I did yesterday too?