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How did Guanabara state become part of Rio de Janeiro state in 1975?

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Aerial view of Rio de Janeiro, Brazil, showing the city's buildings, Sugarloaf Mountain, Guanabara Bay with boats, and surrounding green hills. — Rio de Janeiro Rio de Janeiro, Brazil.

When the national capital of Brazil was moved from the city of Rio de Janeiro to Brasília in 1960, the territory that had served as the Federal District was converted into the state of Guanabara. This new state existed as an enclave within the surrounding state of Rio de Janeiro.12

In March 1975, the two states were fused to form the reorganized state of Rio de Janeiro. Following this merger, the city of Rio de Janeiro was designated as the capital of the newly reorganized state and became one of the 14 municipalities within the Metropolitan Region of Rio de Janeiro, also known as Greater Rio.12