I don't understand your question. I'm not making any cut-off point, I just said that it was more common in the past for a citizens of a nation to be genetically linked to each other. Certainly that still applies to many countries today.
I’m sorry , I don’t believe that is true. Do you have any sources for your claim? Historically empires had been multi ethnic and multi lingual; with rise of nationalism in mid 1800s onwards we start seeing large population transfers and ethnic cleansing, and forced acculturation, leading to a world today where many modern nation states have only one “ethnic group”.
E.g. 150 years ago there used to be many German speaking villages in what is now Poland. There used to be many Turkish speaking locales in Greece, etc etc.
It obviously depends on where and when, but I think you’d have a difficult time finding any past empires that are as genetically diverse as contemporary Canada, USA, etc. Even as wide spread as say, Rome or the Ottoman Empire were, they had little-to-no representation of Chinese, Japanese, South American, Indian, and so on.
Germans and Poles are more similar to each other than Indians and Colombians.
