I had always thought that the EU originated from the
European Coal and Steel Community, designed as a supranational organisation to prevent France and Germany ever again going to war over the
resources of the Saar Basin.
You do mean the steel industry there. The Saar Basin was one of the two big areas where steel was being produced, the far bigger though the Ruhr Area. Today both of their glory days have been long gone, like for the rust belt in the USA.
Anyway, when the ECSC was founded in 1952, the Saar Basin was still French. The Saarbasin was French two times during the 20th century, first time after WWI until 1935 in a referendum the people there decided in a referendum to become German again, the second time after WWII and they decided in 1955 to become German again, which happened somewhat later.
But you've just got to take an European map, and to think bigger than the Saar Basin; this is a political map of Europe in 1949:
The defining movement of the 19th century have been nation states; Germany came pretty late to this party, France and the UK have been nations long before 1871. Due to Napoleon I. Germany was most of the time in the 19th century fractioned into gazillons of little principalities and alike with a few expections like the very militaristic state of Prussia, until Bismarck started the unification without Austria.
Germany is in the heartland of Western Europe, and has today 9 neighbors; most of Germany is a nice, wide plain. When Germany became a nation, and industrialized, in the 20th century Germany started two world wars - and lost both of them. The history of Europe is being driven by the status quo of Germany - when it's too weak, the rest of Europe suffers economy wise, when it gets too powerful or builds an snappy army its neighbors are looking again at least a bit skeptical on this what the heck is going on because of the history. On the other hand in order to stop the spread of communism to the west, they also wanted a prosperous Germany; but such a thing just might become warhungry again, that was one major fear, because it started two world wars within 25 years only. So the not unjustified fear was that history might repeat itself a third time, and this was something to avoid.
So the idea was to integrate all of Western Germany into a bigger framework with its most important neighbors, which back then were still considered as heirloom enemies like France or the UK, to make sure that there is one Western block against communism in the east, and also ensure that the Germans don't want to play war again too soon. This is why the NATO, but also the ESCS came into existence; the Saar Basin was only a small part of the reasoning, embedding Western Germany as a whole into the west was by far means the more important task they wanted to achieve, to ensure peace, but also to ensure that Western Germany does not decide some day on its own to become part of the back then communist GDR, or a neutral country like Austria.
In fact during the 1950s the USSR offered the unification to Western Germany, but insisted on a neutral status of total Germany; something which Adenauer refused.