How Nation-States came to be

Nation States are states by people for the people. First such states emerged only recently. The US was first such state and France after Friench Revolution was second. The UK after beheading of King Charles I and Dutch Republic could be considered prototype nation states.

Before French Revolution France was King's State or Kingdom. Louis XIV famously said Etat c'est moi or 'I am the state' in English. He meant it very literary, as it he owns France as if a private property does what he wishes with it. Back in the days of Louis XIV this was norm and most other states in Europe and the world functioned this way. They were states of the monarch and his loyal servants and for the monarch and his loyal servants. 

Sure, even Loius XIV had to share spoils of the state with his subordinates to keep them loyal. These servants were the top-down close shop elite of the state who were the only one who benefited from the state.

French Revolution changed that. During the course of revolution people of France obtained self-consciousness as nation and wrested control of their country from their King. King and his supporters however did not want to give their country away, so a fight ensured, Louis XVI, a successor to the XIV, was even beheaded as revolutionaries suspected he wanted his country back.

Once things in France settled in revolutionary way, other countries in Europe felt alarmed that these developments in France set a dangerous precedent that will put their own rule in question. At these times no country in Europe had any form of legitimacy that stemmed from its people. All of them were also a King's and elite's states that worked on for elites. The elites were afraid that when people learn of developments in France they too will wish to have a stake in the system, to make it work for them. Elites did not want to share power with the populace.

Thus, former enemies put their differences aside and united in containing an idea of nation state for good. They defeated Napoleon and restored the rightful monarch to French throne as per King's state principles of the old. 

Back at congress of Vienna they all thought that they destroyed the dangerous ideas of Friench Revolution and things will come back to how they used to be. King's and their elites will go on to governing for themselves as they always did. 

They were wrong. Idea of a nation state did spread all over the Europe. Just 15 years afterwards France again overthrew the king and replaced him with more popular pretender. Over the rest of 19th century half of the Europe followed the suit and transformed into nation states.

Those who resisted this change, like Austria (later Austria-Hungary) for example, only managed to hold out until WWI and fell apart in nation states at the end of the world.

The idea took much firmer root over the 20th century and by now most of Europe and Western world in general consists entirely of nation states. That became so normal that some do not even understand how it was before this change.

Seeing the trend, many non-nation states started to adopt some trappings of a nation state in order to disguise themselves as nation states. They hoped doing so will avert revolution and full transformation into a nation-state. Fundamentally however these disguised non-nation states only strive to preserve their systems of rule of the elite. The distinction between nation-states and non-nation states did blur.

Over time they became so paranoid that revolution will happen in their country and kick them out of power, that grew to think that nation states as a group want to destroy them. Just like they used to vehemently oppose Napoleon simply out of principle that he has no right to rule a country because he was not of royal blood. When Russia, China, North Korea and Iran complain that the US sponsor the protestors in their countries, that is because of that paranoia.

However, revolutions happen from the desire of people of the countries to have a stake in the country and not be pushed aside by the elites who think they are better than common people.

By the turn of the century there are still many non-nation states here and there, they are mostly outside of Western World. Countries that border Western World of nations states, such as Russia or Belarus but not nation states themselves attract most attention. Particularly those where there is ongoing struggle between people and governing elite, like Ukraine and Belarus. However, there are many others.