Nationalism is often blamed for wars and strife. But, a 2011 study argued that accurate alignment of political and geographic boundaries with ethnic, religious and national identities was a powerful predictor of the absence of those things.
The idea is starkly at odds with the American ideological commitment to multiculturalism, diversity and the "melting pot", yet is institutionally embedded in our political DNA as a federal state. In contrast, the idea is much more mainstream in Japan and in many European nations that are built on nationalist foundations. And, it is widely acknowledged in political science circles that one of the important factors that caused newly independent European colonial states to fail was their lack of congruity with a national identity.
For example, Nigeria experienced a civil war based on east-west ethnic differences shortly after its formation, and is now experiencing a genocidal ethnic and religious conflict between Muslims in the North and Animists and Christians in the South near their geocultural boundaries in the Northern Nigerian states.
A more skeptical view of that premise is found in the high concept Young Adult novel/political fable "Feuds" (2014) by Avery Hastings, told in part from the perspective of the daughter of a politician who favors the segregation of biologically and educationally enhanced "Priors" and non-enhanced "Imps" (for imperfects) in the 22nd century city of Columbus.