An enclave I missed!
I thought I was familiar with all the odd little
enclaves and exclaves that existed in the '50s and '60s, but here's one I missed!
Barentsburg was mentioned in a news item about Russia's latest claim to a large section of the Arctic. It's a little piece of Russian territory on the otherwise Norwegian Svalbard islands. Barentsburg has been Russian since 1920, but hasn't been used or settled continuously. It was depopulated in WW2, then grew to more than 1000 people in the '70s. Since the end of the USSR it's declined, but still has about 300 residents. Not a military installation, more like a mining camp or a company town.
After perusing the list linked above, I see a pattern of sorts. En/ex/claves often emerge from conflicts. Many new ones were generated by the Yugoslav and Nagorno-Karabakh wars of the '90s. But after they form and crystallize, en/ex/claves often cause a linkage between former enemies. When some of Group A is stuck inside Group B, A has to figure out how to get along with B. This doesn't work when A and B have cultivated centuries of grievances, but in other circumstances it may work.