Earlier quoted context omitted.
>Disclaimer: I'm a child of English parents who was born in Wales but grew up in Scotland. I have Scottish and English children, in-laws and cousins. I have a family home in Scotland but I currently live in England. My children live in England and Scotland. Some of us live in Italy. // This may be an indication of the problem. To my view your opener should be "I'm a child of British parents, born in Britain and grew…
I would have but that would have made things very confusing: I feel 100% British. My immediate family is scattered around the UK our forefathers were scattered throughout the British Isles—one half of the family was Irish. Even my English parents have Scottish blood somewhere down the line. Even worse for me, I'm an internationalist and I felt very proud to be part of the EU for many of the same reasons I felt proud…
"Ethnic countries" - if the states primarily contains one nation of people - ethnically (ie mainly culturally), is commonly referred to as a national state.
National states became a popular concept in the 19th century, possibly because the kings, emperors and other rulers were starting to loose power and had to build their states around some concept. Before that, the kings and the rulers did not give the nationality of their subjects much of a thought I suppose.