From a systems perspective, nation-states and empires arise when they are superior solutions to security compared to whatever arrangement they replace: feudalism, warlords, tribal confederations, etc.

States and empires fail when they are no longer the solution, they are the problem. As the book The Upside of Down: Catastrophe, Creativity, and the Renewal of Civilization explains, when the dissolution of the state / empire becomes the pain-reducing solution, the inhabitants withdraw their support and the empire loses its grip and expires.

As I explain in my new book, Global Crisis, National Renewal, states and markets are problem-solving structures. These structures solve problems by optimizing adaptability and beneficial synergies that reinforce one another as evolutionary advances.