Punctuation

Because those are both Independent Clauses. Complete senteces in their own right. Using only a comma to divide them creates a "comma splice". I try to avoid semi-colons in my writing (as a matter of style, not because they are incorrect). I would use a period and make two sentences. Actually, I would rephrase it a make it more concise. You repeated the word 'some' in the first sentence, which makes it uncomfortable (in my opinion).

Some survived and gained privilege, others did not.