In Russia, Germany, and China, practically everywhere the cities had been existing only because there was a steady supply of new population moving into the cities from the country. I once read an article analyzing the demographics of modern cities. This article claimed that the overwhelming majority of the modern urban population in all the world's cities, their grandparents, or grand grand parents came from the village. In other words, almost all of the modern urban dwellers can trace their ancestry to rural dewllers who immigrated into the cities not more than three or four generations ago. There are almost no urban dwellers who can trace their ancestry to other urban dwellers for more than four generations. In other words, the urban dwellers of for example the early 19th century have no genetic continuity with modern urban dwellers.He does mention how populations and fertility contract when people move to cities.
The conclusion of this article is that the urban populations have been slowly dying out over the generations, and that the cities have been replenished only by new rural immigrants in each generation. This means that if there wouldn't have been any rural immigrants at all, then the cities would have slowly died out and become abandoned.
The cities are artificial constructs, existing only at the expense of the rural areas, relying on them both for food imports, as well as replenishing the population.