The modern nation-state is a political entity that was created at the end of the thirty years war by the Peace of Westphalia. This new concept recognized geographic boundaries of a nation and that nations should largely be free of outside influence. Also, that the nation was the primary, cohesive entity with common internal interest that negotiated with other nation states that have their own interests. The idea of empire became passe', particularly as related to a single sovereign person (king, emperor) or one of a religious state that ailed with a particular religious sect.
The essential properties of a nation-state are:
Sovereignty: being independent from other nations.
Independence of the influence of external agents, either other nations or others.
Have relations with other nations. The nation is the primary negotiating entity.
Has a population of citizens. These folks have rights and responsibilities to the nation.
Has a geographic boundary. The nation controls the land within its boundaries.
Has a national currency. Controls and regulates the values of the currency used by the nation.
Has a common culture. Common values, rituals, symbols, mythology, and history.
System of laws aligned with the culture.
A national defense to defend against other nations which could be hostile.
The United States of America, one could argue, became by the mid-twentieth century, the purest realization of the ideal of the nation-state. It kicked out the british king and became sovereign. It kicked out the british to get rid of external agents (at least they tried). It formed relations with other nations, e.g. France. Americans then thought of themselves as, well, Americans rather than brits. The borders were the combination of the state boarders. They eventually created a national currency, but that took some time. By mid-twentieth century the US had a culture that bound its citizens (most of them at least) together with a common identity. It had laws which reflected this culture and the founding principles of the rights of man. And it developed a military in WWII that was able to overwhelm fascism. So, the USA became truly a nation-state.
But how does a nation cause those properties to come into being and continue into the future? That is what actions does a nation-state take and what structures does it put in place to actually be a nation-state? Looking back at the list we see that the essential feature of a nation-state is controlling what transits boarders. That is, what leaves and enters the geographic boundary of the nation. Control over boarders is how the nation-state puts into effect the properties to be a nation-state. In a sense, a nation is defined by its borders and the control thereof. Well, what transits borders? People, goods, services, money, communications, ideas. These elements that transit borders are mostly economic and financial in nature. So, being a nation entails border concerns with economic and finance issues as well as political issues. So the opposite must also be true. That is, nations which don't control their borders are no longer sovereign.
The US used to control these boarder crossing entities quite strictly, as do all sovereign nations. Entering and leaving the country was controlled by strict visas on how long one could visit. And for work, relatively few could enter and stay on a temporary basis. Entry for work was predicate upon intent to immigrate and become a citizen. And the right to immigrate was relatively difficult to secure. The currency, i.e. the US dollar, was backed by gold and then by the gold exchange mechanism of Bretton Woods, which ensured its value and stability. Trade was regulated to prevent deficits and protect key national industries by means of tariffs and quotas. Even ideas were regulated to some extent as certain books and publications were prohibited from import.
Today the situation for the US is much different. No longer are borders so controlled. People flow over the border relatively unimpeded as illegals aliens to work in agriculture and construction. H1-B visa workers come by the tens of thousands for years to fill technology positions because of a supposed shortage of domestic talent. Trade is now almost totally unregulated, so massive deficits accrue year after year. Financial transactions across the border are similarly almost unregulated with foreigners able to buy up property and businesses unimpeded. National defense has become world policing for someone's interests. However, who's interests that is remains a bit unclear.
Many of the essential characteristics of a sovereign nation have been given up by the US over the last few decades. The US really doesn't control its borders anymore. Which makes me ask: is the US still a sovereign nation? and should it even continue to try to be one? Perhaps the globalists are right? or at least are getting their way?