Interesting to look at the UK and Ireland and at some other historical national precedents:
The British Isles: Not especially large total land mass; geographic logic would make sense of all the
British Isles being one nation yet the populations will have none of it.
The Irish historically were several nations before the British arrived and England itself was
too before the Norsemen etc arrived. Scotland too was a proud nation apart
After a few hundred years of being cemented together, the Irish broke away; the Scots are
doing the same in peaceful fashion and the Welsh are working out how to (too).
The lesson to be learned from the British Isles' peoples experiences is obviously that
civilising influence is towards small national countries rather than huge ones.
The USSR's break up points in a not too dissimilar direction as does that of Yugoslavia.
The USA is a conundrum. Maybe it is too new for the civilising trend towards smallness in nation states to be making its effect or maybe it has been so successful up until now that its citizens so far have not been tempted to consider alternatives like down sizing (yet?).
The Italians used to be a collection of nation states but still sometimes seem so eg Siena vs Firenze. The Chinese trend now is towards mammoth nationhood but I know not whether that is how things used to be there as well.
Tentative conclusion: The EU trend towards enlarging and centralising goes against the historical
grain for the British Isles where the trend is towards dividing up into small easier to govern nation states but with sharing common trading markets with friendly smallish neighbours - The EU trend is more akin to that of China today or the USSR of yesterday. The EU might prefer the USA as their precedent but the USA seems far more right wing even now than most of the EU states and I doubt that the patriotic type of French
socialism will prove to be really compatible with being part of a conglomorate nation most of which is not French.