Six countries founded what became the European Union
The European Union grew out of two earlier communities. In 1951 six states signed the Treaty of Paris, which pooled their coal and steel industries in the European Coal and Steel Community. In 1957 the same six signed the Treaties of Rome, which set up the European Economic Community and Euratom. Those bodies are the line from which the European Union descends. The list is fixed: the six were the same in 1951 and in 1957, and nothing now can change it.
Name all six first. Then sort them into their two groups.