Overview
Onam is an annual harvest and Hindu cultural festival celebrated mostly by the people of Kerala. It is traditionally associated with the legend of the benevolent Asura king Mahabali, who is believed to have once ruled Kerala and to return each year to visit his people. A major annual event for Keralites, Onam is the official festival of the state and is marked by a wide spectrum of cultural events.
In 1961, during the tenure of Chief Minister Pattom Thanu Pillai, Onam was officially declared the national festival of Kerala. In the following year, however, large-scale celebrations were curtailed due to the Indo–China War. Despite this interruption, the government's declaration marked a turning point in the public observance of the festival.
From then onwards, Onam gradually developed into a grand public festival celebrated across the state and among the Malayali diaspora. While its roots lie in agrarian harvest traditions and Hindu cultural memory, it is observed today as a shared cultural occasion, with associated traditions, performances and community gatherings forming part of Kerala's public life.
References
Adapted from the English Wikipedia article on Onam.