This is an interesting question with many ways to expand it, and I won’t go far into that. I liked reading Toynbee’s ‘A Study of History’ with the S/R or challenge-response paradigm concerning the development of civilization and the stage it goes through (about four) as part of a cycle of civilization. There are many other theories though- too many to sort through the best for simple answers for a course question unless one knows what they are looking for.
Toynbee believed (among other ideas) that a creative minority stimulates the existence and culture of a state and the uncreative majority follows those values. If the creative minority of founders fades away the uncreative majority’s ideas and culture may evolve obsolescence.
The main point of a modern state seems to be that of a common culture promoted by the state. The U.S. government in the past few decades seems have put some effort into dissolving that common culture in preference for multiculturalism- and that seems apropos of the Universal phase of a civilization aka globalism.https://courses.lumenlearning.com/suny-hccc-worldhistory/chapter/introduction-to-nation-states/
One may of course discount that point about culture and place the being of a modern state in institutions, financial structures and laws. Developing nations famously tend to lack adequate non-governmental institutions or to have weak ones. Consider the value of Universal free public education to the intellectual capital of a modern nation-state and the perpetuating poverty of nations with weak educational institutions.
Some may believe that the world culture is a modern nation-state that has transcended national boundaries. The heterodox global financial structure might support that thesis.