In 1648, Europe became the birth place of the contemporary nation-state system. This event was result of the Westphalia Treaty between the European countries that remained engaged in 30 years of unending war. Following the war, the countries decided to respect each other's boundaries and governmental sovereignty. From that point onward, the idea of modern states emerged. But, will there be a point in the future where world states will integrate into a single country? That's not easy to predict. But, if we look at the unions like European Union, some positive and encouraging hope can be expected.
Contrarily, EU is also falling. United Kingdom is soon going to be detached from its union. This reflects that the world is actually moving towards further division into the state rather than getting united into a single state. Similarly, President Trump of the USA speaks of building border walls and engaging in more protectionism when it comes to trade. With such trends rampant in the world, it can be assumed that the nations will not join in forming a single state. But, that is not the last word in this regard. It is yet to be witnessed how future political course of the contemporary states will be.