After the declaration of Indonesian independence in 1945, the eastern part of Indonesia declared the State of East Indonesia. The state was further included in the United States of Indonesia as part of the agreement with the Dutch contained in the transfer its sovereignty to Indonesia in 1949.
In 1950, United States of Indonesia dissolved itself into a unitary state and began to divide its component area into provinces. In 1958, by Indonesian law (Undang-Undang) No. 64/1958, three provinces were established in the Lesser Sunda Islands, namely Bali, West Nusa Tenggara and East Nusa Tenggara. The area of East Nusa Tenggara province included the western part of Timor island, Flores, Sumba and other several small islands in the region. The province was sub-divided into twelve regencies and the City of Kupang, which had regency-level status.
Following the fall of the Suharto regime in 1998 and the passage of a new regional autonomy law, there was a dramatic proliferation (known as pemekaran) of regional governments across Indonesia (at both provincial and regency level). Several new regencies were created in East Nusa Tenggara by the division of existing regencies: