The Republic of the United States of Indonesia (Indonesian: Republik Indonesia Serikat (RIS)) was a federal state to which the Netherlands formally transferred sovereignty of Indonesia on 27 December 1949. This transfer ended the four-year conflict between Indonesian nationalists and the Netherlands that was fought over for control of Indonesia. At the same time, the Federal Constitution of 1949 came into effect.
The RUSI comprised sixteen state entities: the 'Republic of Indonesia', consisting of territories in Java and Sumatra with a combined population of almost half of the whole RUSI, and the fifteen states established by the Dutch, which had RUSI legislature that was far in excess of their populations.
Over the first half of 1950, the non-Republic states gradually dissolved themselves into the Republic. The United States of Indonesia was officially dissolved and replaced by the Republic of Indonesia, a unitary state, by President Sukarno on 17 August 1950, the fifth anniversary of his proclamation of independence.