Organisation of Eastern Caribbean States was founded on June 18th 1981 under the Treaty of Basseterre
Background
The Organisation of Eastern Caribbean States, or OECS, is an International Inter-governmental Organisation working for regional integration in the Eastern Caribbean.
The treaty that created it was signed by seven Eastern Caribbean countries on June 18th 1981, to promote unity and solidarity among the Members.
The Treaty of Basseterre takes its name from the capital city of Saint Kitts and Nevis, where the signing took place.
A Revised Treaty of Basseterre replaced it in 2010 and created an economic union.
The signing took place in Saint Lucia on 18th June 2010, at the 51st Meeting of the Authority.
The newer treaty sets up a unified financial and economic space, with free movement of goods, people and capital.
The OECS is described as a Regional Grouping of 12 countries, with 7 Protocol Countries and associate members including the British Virgin Islands, Anguilla, Martinique, Guadeloupe and Saint Martin.
In plain words
OECS Organisation of Eastern Caribbean States — An inter-governmental organisation for regional integration in the Eastern Caribbean.
Treaty of Basseterre Treaty of Basseterre — The 1981 founding treaty, named after the capital of Saint Kitts and Nevis.
Protocol Countries OECS Protocol Countries — The member states whose citizens may travel and live in any member state with a valid form of identification.
Economic union Economic union — An arrangement removing trade barriers for a single market with a customs union.