|Map of the Commonwealth of nations. Based on Image:BlankMap-World6, compact.svg with information from List of members of the Commonwealth of Nations and colour scheme from Image:Commonwealth of Nations.png. Commonwealth of Nations members Suspended Commonwealth of Nations members (Fiji) Former Commonwealth of Nations members (Ireland and Zimbabwe) British Overseas Territories and Crown Dependencies (Photo credit: Wikipedia)|
How did India join this Commonwealth? The British ruled India from 1858 to 1947. However, repression by the British government and a strong sense of nationalism led many to non-violent protest for self rule. One prominent figure amongst non-violent protestors is Mahatma Gandhi. In 1942, the British government attempted to offer India independence in exchange for its support in World War II, but notable figures like British prime minister Winston Churchill opposed this move, and therefore negotiations fell through. Following in July 1942, the Indian Congress called for the complete withdrawal of the British from India, referred to as "Quit India." Such Congress leaders were arrested, and violent protests formed sporadically around the Indian subcontinent.
Finally, at the end of World War II with the new British Labour Party now leading the United Kingdom, India was granted independence in 1947. Following the war, the UK faced an economic burden and was unable to uphold its overseas empire. But brewing tensions amongst the Hindus and Muslims of the subcontinent also led to a partition at this time into two independent nations of India (the 'Hindu' half) and Pakistan (the 'Muslim' half). This formation of an independent Indian republic brings India to where it is today.
Now as a part of the Commonwealth of Nations, India participates in many of its member events. India was in fourteen of the previous eighteen Commonwealth Games (a sports competition/celebration amongst member states) and even hosted the 2010 games in New Delhi. Though only nominally ruled by the United Kingdom today, India still enjoys a friendly relationship with the UK and other memberships under the Commonwealth.
Sources: Wikipedia, The Commonwealth.org, cwgdehli2010.org