colonisation libre

Hello everyone,
Not sure how to translate this in the following sentence:
Possession française depuis 1853, une colonisation libre et pénitentiaire s’y développe,

I want to use "penal colony" for pénitentiaire and would be repeating myself to use "colony" or "pioneer colony" for colonisation libre.
My attempt is :
After French possession in 1853, a colony and prison colony developed (the rest of the sentence continues (to the detriment of the native population).

Any ideas please?
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