I wonder if the nation-state hasn't outlived its usefulness.
City-states had largely disappeared by the time of the Enlightenment. By the time that Germany and Italy became nation-states in the late 19th century, most of the West had coagulated into nation-state form. A nation-state had more military power than a city-state and by eradicating trade barriers within the country, nation-states stimulated trade and prosperity. Conditions of the 18th and 19th centuries seemed to make the city-state obsolete; perhaps the conditions of the 21st century will make the nation-state obsolete.
In today's world, the nation-state seems increasingly ineffectual at dealing with real problems. It isn't particularly suited to the major issues of the present. Pandemics, terrorism, financial crisis, immigration, trade, economic prosperity and, of course, global climate change are all issues that thumb their noses at national boundaries. Already in Europe, nation-states are gradually giving more power over to the EU. I suspect that this is a trend (that will, as all such trends, suffer reversals).
It is difficult to think of what nation-states are still uniquely suited to do; they still seem to have a monopoly on starting truly horrific wars. We now have about 200 nations on this little planet. It's not obvious that we can afford for even 10 or 20 percent of them to be strutting around with nuclear-equipped armies. It might make sense to emasculate the nation-state before this creation of ours destroys us.
“If you said, ‘Let’s design a problem that human institutions can’t deal with,’ you couldn’t find one better than global warming.”
- Henry Jacoby, MIT School of Management