What is relation between class and ethnicity?

Each culture has it's own class system, some very well defined, and others (like in the US) not very clear at all. However, this happens amongst all ethnic groups that I am aware of, to greater or lesser extents.

Where differences happen is when the culture of one ethnic groups comes to dominate another. 300 years ago, Arabs and blacks in Africa captured blacks, and sold them to Europeans, who took them primarily to the Americas. Thus, a white person would be in a higher class than black one, automatically. This held true for a long time, and some still think that way today. In the same way the Japanese dominate the Ainu, a white aboriginal trip in Northern Japan. And so one. There are many examples. In Bermuda, British whites are on top, the Portuguese merchants are the middle, and blacks are at the bottom.

But, these are due to the histories of domination, and are by accident, not ethnicity. I do not think you can make a connection between the two that holds universally. Perhaps in one country or areas, but somewhere else, the situation might be reversed