The idea that some human groups are innately different, due to innate characteristics or the circumstances they live in, has a long history. It became strongly associated with scientific racism in the 19th century and is now widely discredited. Those who still argue credibly for some sort of innate natural difference as the basis for nations usually opt for a relatively soft version of this, emphasising issues like kinship loyalty.
The world is divided into distinct ethnic communities which constitute nations. These ethnic communities are shaped and made distinct by territorial and biological factors. The sort of territory which a group inhabits shapes their cultural character. Biological factors are variously attributed to racial distinctiveness or sense of obligation to other members of an ethnic group based on inherited kinship loyalties. Nations, therefore, exist whether or not they have political independence.
Ethnicity is a notoriously difficult concept to define. There is little evidence of territory shaping any identity in any particular way. For example, mountainous regions have produced cultures as varied as Quechua, Karen, and Montenegrin. Ideas of ethnic unity are very dubious. Theory of innate human difference along ethnic lines is widely discredited as a pseudo-science. Ideas of kinship struggle to explain nations which contain many different ethnic groups such as the American nation of immigrants or India which contains over 2000 ethnic groups according to some counts.
[P1] The world is made up of distinct ethnic communities, shaped by material factors and persisting across time. [P2] Nations are formed on the basis of these ethnic groups.
Rejecting the premises
[Rejecting P1] The criteria defining ethnic identity is very hard to describe with any consistency. Ethnicity is not timeless but emerges from historical processes. [Rejecting P1] Ideas about territorial factors shaping human culture and mentality are dubious, and ideas of racial difference are discredited. [Rejecting P1] Many modern nations contain multiple different ethnic groups.