re: conventional wisdom
Yep, the former European countries retreated from the former colonies and at the same time decided to build a common economical market,
6 countries started in 1957. Because it was visibly productive, other countries joined and the market grew and more countries joined and the market grew even more and there's even now a common currency.
Ask anybody from Spain or Ireland what it was before compared with after they joined.
This was all done progressively (so as not to produce major social disruptions).
And the former colonies, well, we'd be only involved if they asked first.
Raoul