Today's date hold a special place in the history of Sikkim as it was on this day mass agitation against the Chogyal rule took off that led to the downfall of the monarchy rule in Sikkim. The agitation was of a result, “due to serious differences which ensued with the demand of repoll in one booth by Kazi Lhendup Dorji and Mr. Krishna Chandra Pradhan, as such the Chogyal had to face the people’s agitation launched by the Joint Action Committee with the tacit blessings of the Government of India. This people’s political movement spearheaded by Kazi Lhendup Dorji finally resulted in Sikkim joining the mainstream as 22nd State of India in 1975(sikkiminfo.net)”.
I was going through an article "Lesson of democracy from Sikkim" by Carleton Cole that recapitulates the movement of April 73 Agitation. Cole writes, "In April 1973 after making allegations that a round of elections had been rigged in favour of the Bhutia thus making ethnic Nepali Sikkimese protested en masse in front of the king's palace, demanding civil rights and the sidelining or even removal of what they called the "feudal" monarchy. Having isolated himself by stubbornly refusing to compromise, Palden Thondup Namgyal, the last king of Sikkim, ultimately caved in and signed the May 8 (1973) Agreement.
The document called on India to provide a chief executive, and to hold elections for an assembly under the "one man, one vote" system, but with the condition that no one party dominate. Essentially this meant enfranchising the Nepali majority, latecomers to Sikkim that they were, while protecting classical Sikkimese (Bhutia) and native traditions of the Lepcha people. The agreement was the first step in a process that would lead to the Sikkimese populace voting overwhelmingly in favour of union with India in a 1975 referendum".
Another article on the said movement writes "In April 1973, the trouble which had been brewing between the Lecpha-bhutia factions and the majority Nepalese group erupted into a political furore of riots. The Nepalese were demanding an election format of “one –man, one –vote”. Once more, the Chogyal had to seek the help of India to restore order and thereafter an agreement was signed whereby the Chogyal’s status was father reduced .he now became virtually a titular head, real power having shifting into the hands of India and to the majority group. Kazi Lhendup Dorji, a man well-known for his anti-monarchist sentiments and his pro-India bias, was elected to the council of Ministers".
An agitation in April 1973 resulted in the merger of the Sikkim Janata Congress and the Sikkim National Congress. The United Party subsequently obtained an overwhelming majority in the general election by securing 31 out of 32 seats. This gave a massive mandate to Kazi Lhendup Dorji to form a new Government.
A C Sinha in”Search for Kirat Identity trends of De-Sanskritazation among Nepalmul Sikkimese" writes by the end of 1960s the last ruler of Namgyal dynasty, Palden Thondup Namgyal, began to nurse an ambition of membership to the United Nations Organization (UNO) for Sikkim and this made him desperate to identify more and more with the vanishing Bhutia practices as the Sikkimese practices. This design was not appreciated by bulk of the Sikkimese masses, which were discriminated by the ruler in favour of the arrogant Bhutia aristocracy and bureaucracy. The situation was so explosive that a small controversy with reference to counting of the votes at Gangtok after 1973 election was good enough to ignite frayed patience of the political activists for cancellation of the election and launching a movement for political reforms. The ruler ignored the demands and went ahead with the preparation of his golden jubilee celebration as the national day on April 4, 1973.
Within no time the agitation spread to the interior and agitators established people’s regime at places after chasing away the state functionaries from their posts. The newly formed political outfit, Sikkim Janata Congress, spear-heading the agitation, articulated the popular aspirations by demanding: full-fledged democracy, a written Constitution, fundamental rights, one man one vote principle based on adult franchise, and abolition of the notorious ‘parity system’.
The agitation turned violent and the ruler lost all his control on the state. In the circumstances, for the second time after 1949, the ruler of Sikkim had to request the Government of India to take over the administration of the state”.
In April 1973, an anti-Chogyal agitation broke out; the agitators demanded the conduct of popular elections. The Sikkim police were unable to control the demonstrations, and Dorji asked India to exercise its responsibility for law and order and intervene. India facilitated negotiations between the Chogyal and Dorji, and produced an agreement which envisaged the reduction of the Chogyal to the role of a constitutional monarch and the holding of elections based on a new ethnic power-sharing formula (Wikipedia).