Accession Day
An Accession Day is usually the anniversary of the date on which a monarch or executive takes his or her office. The earliest records of accession celebrations date from the reign of Queen Elizabeth I of England, and the custom is now observed in many nations.
Accession Day in India's Jammu and Kashmir commemorates the day in 1947 when the area joined the Dominion of India.
Belgium
In Belgium there are local celebrations of the reigning monarch's accession, but the anniversary of the accession of the first King of modern Belgium, Leopold I, on 21 July 1831, is celebrated as a full national holiday, known as "Belgian National Day".
Indian subcontinent
Accession Day is a state holiday in India's northernmost state, Jammu and Kashmir, commemorating 26 October 1947, when Maharaja Hari Singh signed off the Instrument of Accession, in which Jammu and Kashmir joined the Dominion of India. (This was part of the series of events of 1947 by which rule in the Indian Empire exercised through a Viceroy as representative of the King-Emperor George VI was converted into the two new Dominions of India and of Pakistan (Pakistan having two territories separated by the whole of northern India). As a Hindu ruler of a state with both Hindu and Muslim subjects the Maharaja's decision was crucial.