residents automatically became Indian citizens on 20 December 1961 unless they had made a written declaration before this date stating their intention to retain their existing nationality. Portugal did not recognise the annexation of its former Indian territories; persons born in applicable areas before 3 June 1975 were recognized as Portuguese citizens. Accession of Sikkim The Kingdom of Sikkim was an autonomous monarchy in northeastern India from the 17th century to 1975. Although Britain (and later India) had control over its foreign affairs, Sikkim was never considered a princely state and always held full autonomy over domestic matters. Sikkim lacked codified nationality legislation until 1961, when the Sikkim Subject Regulation came into force. This legislation initially defined Sikkim subjects as anyone of native ancestry with their permanent home in the country, or a person permanently settled in Sikkim who had cut all ties with their previous country or had acquired immovable property in Sikkim. Subject status was further restricted by a requirement to have held property rights in Sikkim before 1937, effectively barring a large number of Nepali residents from obtaining a permanent status in the country. Dual citizenship was prohibited and women automatically lost their rights as subjects on their marriage to non-Sikkimese men. The ethnic qualification to subject status was particularly unpopular, leading to a revolt and the repeal of the regulation in the following year. However, the 1962 amendment also created a facilitated naturalisation pathway for non-subjects of native ancestry; any person descended from a person domiciled in Sikkim before 1850 could apply for subject status even if they did not live in the country. After the dissolution of Sikkim's monarchy and its accession to India in 1975, any person registered as a Sikkimese subject before 26 April 1975 became an Indian citizen. This process of acquisition left certain groups of people living in Sikkim stateless including long-term residents without property, Sikkimese women who married non-Sikkimese, and individuals who had otherwise qualified for subject status but failed to complete registration before 1975. Legislative responses to migration Indian nationality regulations were broadly permissive when they were first created at the time of the republic's founding. Successive governments since the 1980s have gradually increased the difficulty of acquiring Indian citizenship in response to changing patterns of immigration from neighbouring countries. Large-scale migration into Assam from Bengal began during colonial rule. British authorities encouraged workers from outside the region to