Rightly or wrongly, and in no particular order, those three aid in class assortment to one degree or another in all societies. I realize you referred to wealth and your reference is correct but wealth also can be a determinant in some societies.
Avoid purely western thought in your effort; for example, it is often said that in the west, persons amass wealth so that they may influence power; elsewhere in the world men seek power so that they may amass wealth.
Skin color is not purely racial difference, it applies as well, perhaps more pointedly from your analytical standpoint, to stratification within groups.
Education is a determinant throughout the world -- and, in different parts of the world, the type of education can make a significant difference. Stratification on educational lines is more severe in the west than elsewhere.
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