European Coal and Steel Community

The European Coal and Steel Community (ECSC) was an international organisation serving to unify European countries after World War II. Formally established via the Treaty of Paris in 1951, the ECSC originated via the signatures of Belgium, West Germany, France, Italy, the Netherlands, and Luxembourg. It was the first international organisation to be based on the principles of supranationalism, ultimately forming the original foundation for the European Union.
It comprised four key institutions:
High Authority: comprised of independent appointees
Common Assembly: comprised of national parliamentarians
Special Council: comprised of national ministers
Court of Justice: comprised of judges from multiple nations
These would ultimately form the blueprint for today’s European Commission, European Parliament, the Council of the European Union and the European Court of Justice.
The ECSC was joined by two other similar communities in 1957, the European Economic Community and European Atomic Energy Community, with whom it shared its membership and some institutions.