In short, every group, every nationality, should be allowed to secede from any nation-state and to join any other nation-state that agrees to have it. That simple reform would go a long way toward establishing nations by consent. The Scots, if they want to, should be allowed by the English to leave the United Kingdom, and to become independent, and even to join a Gaelic Confederation, if the constituents so desire.
A common response to a world of proliferating nations is to worry about the multitude of trade barriers that might be erected. But, other things being equal, the greater the number of new nations, and the smaller the size of each, the better.
In sum, if we proceed with the decomposition and decentralization of the modern centralizing and coercive nation-state, deconstructing that state into constituent nationalities and neighborhoods, we shall at one and the same time reduce the scope of government power, the scope and importance of voting and the extent of social conflict. The scope of private contract, and of voluntary consent, will be enhanced, and the brutal and repressive state will be gradually dissolved into a harmonious and increasingly prosperous social order.