Annexation and Statehood

In 1975, the Prime Minister of Sikkim appealed to the Indian Parliament for Sikkim to become a state of India. In April of that year, the Indian Army took over the city of Gangtok and disarmed the Chogyal's palace guards.
Thereafter, a referendum was held in which 97.5 percent of voters supported abolishing the monarchy, effectively approving union with India.
On 16 May 1975, Sikkim became the 22nd state of the Indian Union, and the monarchy was abolished.