I generally avoid dividing the data into separate groups. (There are situations that call for separating data, of course.) I think about a model that might use all the data for the most power and sensitivity, but also account for group differences, if they exist. So what about a linear model that includes ethnicity and the group as effects?
Another consideration is the partition method. This model will tend to find the levels that should not be split.
Have you tried using two-dimensional hierarchical clustering?
Finally, ANOVA is useful when you are testing for a difference. it is not intended when you are testing for similarity. Lack of a significant ANOVA is not evidence for similarity. Equivalence testing is also a one direction test, but in the opposite direction.