Scotts and English are different people; so are Walloons and Flemish; so are Catalans and Spaniards; as of course Greeks and Germans, or French and Finns. These movements are not "separatist" but "national".
"When in the course of human events it becomes necessary for one
people to dissolve the political bands which have connected them with
another ..."
So begins the Declaration of Independence of the 13 colonies from the king and country to which they had given allegiance since the settlers first came to Jamestown and Plymouth Rock.
The declaration was signed by 56 angry old white guys who had had enough of what the Cousins were doing to them. In seceding from the mother country, these patriots put their lives, fortunes and honor on the line.
Four score...
The countries of Europe were not mono-racial. There are many different kinds of Germans; the French comprise Gallic predecessors, germanic Franks, and other western Germans; the English comprise French Normans, Danish, Anglo-Saxons, Britons and others; the UK of course is even more diverse; Italy is such a diverse mix of peoples that at one time the definition of 'Italian' was viewed as nothing more than a convenient construction.
Nationalism cements diverse groups into one.