[hga]

I think you're really stretching the definition of prison, e.g. it was also a cage that 25% were given permission to leave.

Why not use internment instead?

[yummyfajitas]

Internment is a special case of imprisonment - all internment is imprisonment, but only some imprisonment is internment (when it's done to large groups without a trial).

[hga]

Yes, but prison, the word we've been discussing up to now, has different and much more loaded connotations than imprisonment.