* Nordics: Iceland and Norway which are ambivalent, despite repeated attempts to get them to join. (They are already in EFTA.) Greenland and the Faroe Islands fall more under the dependencies category below.

* Switzerland which can't because it wishes to be neutral, and also because of the finance sector. The Vatican has some similar issues.

* Microstates, dependencies and tax havens.

* Ex-USSR. The Baltics function well in the EU and are the exceptions, but Moldova, Belarus, the Ukraine and Russia each have massive issues. (Including how Moldova doesn't control much of its territory and much of Belarus is contaminated by Chernobyl.)

* The Balkans. Problematic recent history. I think Albania and North Macedonia may join in the near future. Serbia, Montenegro and Kosovo have ex-USSR style issues.

* Turkey.

* The UK, which is problematic since it is the only major state which has left.