Red: Thathegrun, the Sea People
Blue: Yivagrun, the Mountain People
Yellow/Brown: Sangaegrun, the Southern People
Green: Thapegrun, the Spear People
The Sangaegrun were the earliest people to arrive in the Valley. They arrived in four waves, continuously, during the lifetime of the Thingatha Empire of the Slithi Waste. These were a dark people, ranging from dusky to jet-skinned. During the first migration, they settled the entire Valley basin, from the very north to the very south, but there were only concentrations approaching any mass around the southern edges of the Sea of Yer.
The Thapegrun were the second people to arrive in the Valley, and they did so in two very large waves. They are from the far east, pale of hair, and pale of skin. They had some knowledge of ships, and established a few proto-states in the north of the Valley, eventually settling on the northern shores and spilling into the southern regions somewhat later.
The Thathegrun came in a single massive influx, and used their ships to settle on all the islands of the Sea of Yer. They also intermarried heavily with the Sangaegrun, though they still have a noticeably olive complexion.
The last to arrive were the Yivagrun, who tend to be shorter than the rest, and possessed of red or brown hair and green or brown eyes. They settled primarily along the western shore of the Sea of Yer, and immediately began trading with their neighbors.
In the modern era, it is slightly more likely to find descendants of the Yivagrun in the west, the Thapegrun in the east, and the Thathegrun in the north, but there has been such intermingling that the descent of a person is not strictly related to their location in the Valley. And indeed, these ancestral tribes are no longer a method by which anyone identifies; the ethnic understandings of the dwellers in the Valley stem directly from the kingdom and region of their birth, rather than the ancestral dependency of their tribe.
If you were going to use the Valley Kingdoms as some sort of Hârnrule setting, you might want this chart:
Ancestral Stock (predominant)