Both the EU and UK would do well to heed the lessons of the League of Nations when it comes to membership withdrawal.
Like the League of Nations before it, the UN is often dismissed as a powerless talking shop or a proxy for the great powers. It's much more than that.
In the 20th century, governments considered the “total abolition” of passports as an important goal and discussed the issue in several international conferences.
The leaders of Islamic State do not see their caliphate as an exercise in theocracy for its own sake, but as an attempt at post-colonial emancipation.