The Commonwealth is a voluntary association of 53 independent countries, almost all of which were formerly under British rule.
The origins of the Commonwealth come from Britain's former Empire. Many of the members of the Commonwealth were territories which had historically come under British rule at various times by settlement, conquest or cession. The administration of such colonies evolved in different ways, to reflect the different circumstances of each territory.
After achieving independence, India was the first of a number of countries which decided that, although they wished to become republics, they still wanted to remain within the Commonwealth.