Remember that the men who founded the European movement had just lived through the greatest war the world had ever seen. The older ones had also lived through the second greatest war the world had ever seen. Nothing was more important to them than preventing a recurrence, and so the EU is based on co-operation between democratic developed countries which would draw them together.
They had seen the damage that arises when national, religious and ethnic hatred is encouraged by unscrupulous politicians and the gutter press.