This is an interesting statement. For which there is no evidence. The UK itself is composed of four countries. If the statement were true, the UK could not exist. It does, merrily so.
The idea of what is the largest possible community is historically contingent. Aristotle would think London impossible, England crazy.
When the US was set up, there was a huge discussion (in fact, still in the 19th century) whether this type of construct was possible.
