I think that the importance of a nation as a functioning and cohesive unit can be seen in the case of post- Revolution America. After gaining independence from England, America adopted the Articles of Confederation as its governing constitution. This document pretty much defined the nation as a "loose confederation of states. " States were able to act in opposition to one another and there was nothing in terms of acting in concert or convergence towards a national identity present. Part of this was a result of the fears of the framers in repeating the same conditions of tyranny as existed with King George and England. Yet, while the states had freedom, they lacked a national identity or the need to seek national consensus. This could be seen in the federal government's inability to raise taxes and generate revenue, sorely needed to pay off a debt from the American Revolution. At the same time, the lack of a national focus made the new confederation susceptible to threats from other nations. Finally, when Shays' Rebellion grew in force and magnitude, there was not a coordinated and concerned national response to such an uprising.
I think that this is where one sees the importance of a nation. The need for individual states to act with a singular purpose, while being able to express their own individuality contributes to a stronger vision. This is where tranquility can emerge and prosperous foundation can be present. When there is a lack of this national focus, greater risks to these elements are present.