Simplify the following text for a Grade 11 native English-speaking person.
Original: By the end of 1933 the first Nazi concentration camps had been erected ( at Dachau , Osthofen , Oranienburg , Sonnenburg , Lichtenburg and the marshland camps around Esterwegen ) ; all remaining prisoners who had been held in so-called protective custody in state prisons were transferred to these concentration camps .
Simplified: By the end of 1933 the first Nazi concentration camps had been built ( at Dachau , Osthofen , Oranienburg , Sonnenburg , Lichtenburg and the marshland camps around Esterwegen ) . All remaining prisoners in `` protective custody '' in state prisons were transferred to these concentration camps .