Perhaps it would not be a great exaggeration to say that European integration grew out of war. These two industries - coal and steel - were key to the production of weapons. Therefore, the placing of these industries of the two recent adversaries in World War II - France and West Germany - under general transnational control should have eliminated the possibility of a unilateral arms build-up in one of them. Thus, the material basis for the war was eliminated. This was the logic of the actions in 1950-51 of the recognised founding fathers of European integration - Jean Monnet and Robert Schuman.
Another thing is that by 1951, amid the conditions of the Cold War in Europe, the partitioning of Germany, the creation of NATO and the geopolitical confrontation between the West and the Soviet Union, the possibility of a hypothetical war within Western Europe itself seemed almost unrealistic. Yes, undoubtedly, there was a phantom pain primarily for France, which twice had faced German expansion in world wars. Nevertheless, the geopolitics of the Cold War dictated completely different tasks. At the same time, the practical advantages of integration outweighed the disadvantages, and soon the ECSC members moved from the "militarised" coal industries and began to build a common market in the civil economy as a whole, which was formalised in 1957.
At the same time, it should be noted that integration was by no means the first solution that was proposed by the Western European victors in World War II in order to avoid a new conflict with defeated Germany. It all started with much more traditional forms of control - occupation and external administration. Here in the second half of the 1940s, France and other Western allies, in relation to the coal and metallurgical centres of West Germany (Saar and Ruhr), almost completely repeated what they had already tested after the First World War.