Do nation states have a moral right to exist?

It depends on what you define as moral rights and how binding they are across nations and cultures. You should make those points clear.

Quoting rickyk95

historically, the most common form of organization has been empires wherein the people who inhabitated a given territory were of diverse cultures, religions, and ethnicity.

Modern history maybe, ancient cultures tended to be less diverse in most of these areas.

Reply to rickyk95

If you think about it, historically, the most common form of organization has been empires wherein the people who inhabitated a given territory were of diverse cultures, religions, and ethnicity. With this said, it does not come to me as intuitively obvious that the default form of political organization should be nation states, it seems rather arbitrary doesnt it? The answer to this question puts the legitimacy of all countries' existence on the line.

Historically, the longest period of relative peace on earth was during Pax Romana which lasted 206 years. The facade of a representational form of government with an absolute strong man. The Romans introduced rules for citizens, civil law. Latin which formed the basis for the romance languages, law, western culture in general, can be traced back to the Romans. Was this the best form of government? Or was it the best form of government for its time.

I think it is the latter. Societies change over time, and governments must also change or they will decline. (I think the Soviet Union's demise is an example) There is no "default form of political organization", only that organization which best suits a specific time and place.

Nation-states are, in a sense, the natural form of human organization since they preserve a unified tribal identity alongside enduring bureaucratic structures. Contrariwise, the singularity of empires, which have difficulty efficiently managing varying groups of people of different cultures, and which are prone to internal collapse due to the bad decision of government leaders, are bound to morph and divide into smaller nation-states. Also the advance of technology has a causal relationship with the existence and strength of nation-states.