Europe and its politics is complicated. Here are some multinational European relations/unions/treaties/agreements, and their memberships,
presented with each country/territory sized as a function of its total population (c. 2020).

Programmed and rendered in MATLAB r2019b.

Europe
Council of Europe
European Single Market
EEA
EU Customs Union
Schengen Area
EU
Eurozone
EFTA
CEFTA
Euler diagram of some of the above relationships and others

Data source for population estimates:
https://www.statista.com/ ​