Uninationalism

What you are proposing is basically impossible. People are divided from each other on cultural and political lines. The closest thing to what you're talking about is the European Union, and even there no German wants to be ruled over by Frenchmen or vice versa. There is a sense of national identity that 1. causes the great achievements in history and 2. simultaneously causes all the conflicts. This is the "soul" of a nation, and virtually all countries would rather eat crow than give theirs up. Beethoven was German and Tolstoy was Russian. Their cultural upbringing caused them to work in the way they did, and if you compare German music to Russian, or Russian literature to German, you will see critical differences. You cannot keep those differences, the beautiful things about each nation, if you combine all nations into one.

The enforcement of international laws and standards is actually NOT contingent on every nation uniting under one flag. International law is, in fact, a law of its own, and you can get legal recourse through it. It's used for a ton of things right now. The problem with it is that it is young, undeveloped and extremely political. For example, China disregards international copyright standards, and the Palestinian/Israeli stuff in international law is so biased that you can't really expect either side to take international law seriously. The answer is not to liquidate nations, it's to focus on international law, building it up to the point where some semblance of fairness is enforced, and all nations are made to take it seriously.