When it comes to "one country" - the USSR aimed at that, and from the perspective of hundreds of millions of people, it wasn't the best idea.
Plus, I think that ethnic states are one of the worst inventions of the 19th century, which accelerated a lot after WWI & WWII. I prefer cities where e.g. 1/3 were Polish, 1/3 German, and 1/3 Jewish (as for my pre-war hometown) rather than monoliths. Even in the middle ages, cities had multiple languages and cultures (e.g. German-speaking for trading cities in Slavic and Baltic countries). Right now, even in many multicultural cities, it is often implicitly assumed that there is the "default language" and an ethnic/national/cultural majority.
When it comes to "one country" - the USSR aimed at that, and from the perspective of hundreds of millions of people, it wasn't the best idea.
Plus, I think that ethnic states are one of the worst inventions of the 19th century, which accelerated a lot after WWI & WWII. I prefer cities where e.g. 1/3 were Polish, 1/3 German, and 1/3 Jewish (as for my pre-war hometown) rather than monoliths. Even in the middle ages, cities had multiple languages and cultures (e.g. German-speaking for trading cities in Slavic and Baltic countries). Right now, even in many multicultural cities, it is often implicitly assumed that there is the "default language" and an ethnic/national/cultural majority.