European Union and prevention of war

In the Schumann Declaration in 1950, French Foreign Minister Robert Schumann said

It proposes that Franco-German production of coal and steel as a whole be placed under a common High Authority, within the framework of an organization open to the participation of the other countries of Europe. The pooling of coal and steel production should immediately provide for the setting up of common foundations for economic development as a first step in the federation of Europe, and will change the destinies of those regions which have long been devoted to the manufacture of munitions of war, of which they have been the most constant victims.

The solidarity in production thus established will make it plain that any war between France and Germany becomes not merely unthinkable, but materially impossible. The setting up of this powerful productive unit, open to all countries willing to take part and bound ultimately to provide all the member countries with the basic elements of industrial production on the same terms, will lay a true foundation for their economic unification.

In The Economic Consequences of the Peace (1919) JM Keynes predicted a second world war due to the Treaty of Versailles blocking any form of Free Trade Union:

A Free Trade Union, comprising the whole of Central, Eastern, and South-Eastern Europe, Siberia, Turkey, and (I should hope) the United Kingdom, Egypt, and India, might do as much for the peace and prosperity of the world as the League of Nations itself. Belgium, Holland, Scandinavia, and Switzerland might be expected to adhere to it shortly. And it would be greatly to be desired by their friends that France and Italy also should see their way to adhesion.

It would be objected, I suppose, by some critics that such an arrangement might go some way in effect towards realizing the former German dream of Mittel-Europa. If other countries were so foolish as to remain outside the Union and to leave to Germany all its advantages, there might be some truth in this. But an economic system, to which every one had the opportunity of belonging and which gave special privilege to none, is surely absolutely free from the objections of a privileged and avowedly imperialistic scheme of exclusion and discrimination. Our attitude to these criticisms must be determined by our whole moral and emotional reaction to the future of international relations and the Peace of the World. If we take the view that for at least a generation to come Germany cannot be trusted with even a modicum of prosperity, that while all our recent Allies are angels of light, all our recent enemies, Germans, Austrians, Hungarians, and the rest, are children of the devil, that year by year Germany must be kept impoverished and her children starved and crippled, and that she must be ringed round by enemies; then we shall reject all the proposals of this chapter, and particularly those which may assist Germany to regain a part of her former material prosperity and find a means of livelihood for the industrial population of her towns. But if this view of nations and of their relation to one another is adopted by the democracies of Western Europe, and is financed by the United States, heaven help us all. If we aim deliberately at the impoverishment of Central Europe, vengeance, I dare predict, will not limp. Nothing can then delay for very long that final civil war between the forces of Reaction and the despairing convulsions of Revolution, before which the horrors of the late German war will fade into nothing, and which will destroy, whoever is victor, the civilization and the progress of our generation. Even though the result disappoint us, must we not base our actions on better expectations, and believe that the prosperity and happiness of one country promotes that of others, that the solidarity of man is not a fiction, and that nations can still afford to treat other nations as fellow-creatures?