The land the original tribes lived in was the location of where the Crystal Empire now is. We know that the area around the Crystal Empire has an ongoing snowstorm that was more likely created by magic as the Pegasi cannot control it, nor can Princess Celestia and Princess Luna, Just like the snowstorm the Windigos created. So what if this magic snowstorm is what’s left after the defeat of the Windigos? The hatred between the 3 tribes went on for so long and was so strong that even long after they united and defeated the Windigos the snowstorm in their original land kept raging on. Or maybe the Fire of Friendship only undid the snowstorm in Equestria and not the original land.
As for the Crystal Ponies, perhaps they were originally part of the 3 tribes, but decided to stay instead of leaving to live in Equestria, they found the Crystal Heart and discovered that the Heart’s magic could keep the snowstorm at bay and protect them. Over time the Heart’s magic affected the ponies living in the Crystal Empire and turned them into the Crystal Ponies that we see today. Or maybe their transformation was more instantaneous. After the Heart was found and it’s magic used, it sent a wave of magic that turned the ponies in the immediate vicinity into Crystal Ponies. (Like we see in The Crystal Empire Part 2 and the other episodes it happens in) but instead of the ‘crystal effect’ wearing off like it does for the Mane 6, the Crystal Ponies changed permanently with the ‘crystal effect’ tied to their emotions.