One of the shocking things about reading contemporary literature from places like England, South Korea and Japan, which have huge swaths of population that are extremely mono-ethnic is how intense and bitter the class divisions can be people people who look the same, dress the same, and speak the same dialects. Indeed, if anything, these societies are known for the prominence of their social hierarchies in day to day life.
Conversely, people who have very disparate physical appearances can be undivided socially.
Ethnicity and social class divisions in the U.S. so frequently coincide that one forgets that the latter can exist and be just as cruel and intense without the former.
Another interesting recent study along the same lines noted that a strong sense of national identity increases trust between co-nationals and decreases the extent to which people have greater trust in co-ethnics when a national identity is also shared:
In diverse societies, individuals tend to trust coethnics more than non-coethnics. I argue that identification with a territorially-defined nation, common to all ethnic groups, reduces the degree to which trust is ethnically bounded. I conduct a “lab-in-the-field” experiment at the intersection of national and ethnic boundaries in Malawi, which measures strength of national identification, experimentally manipulates national identity salience, and measures trust behaviorally. I find that shared nationality is a robust predictor of trust, equal in magnitude to the impact of shared ethnicity. Furthermore, national identification moderates the degree to which trust is limited to coethnics: while weak national identifiers trust coethnics more than non-coethnics, strong national identifiers are blind to ethnicity. Experimentally increasing national identity salience also eliminates the co-ethnic trust advantage among weak nationalists. These results offer micro-level evidence that a strong and salient national identity can diminish ethnic barriers to trust in diverse societies.
Amanda Lea Robinson “Nationalism and Ethnic-Based Trust: Evidence from an African Border Region” (2017).