Original: After the transfer, the municipality of Rio de Janeiro became the Estado da Guanabara (State of Guanabara), which existed from 1960 until 1975 when the State of Guanabara and the State of Rio de Janeiro merged, to be named the state of Rio de Janeiro.
Simplified: Afterwards, the municipality of Rio de Janeiro became the Estado da Guanabara (State of Guanabara), from 1960 until 1975.