Original sentence: The United Kingdom has been an important neighbour, was a major member of the European Economic Community since joining in 1 January 1973 (when six countries were members), and was a member of the European Union until it left on 31 January 2020
Edited sentence: The United Kingdom has been an important neighbour, was a major member of the European Economic Community since joining in 1 January 1973 (when six countries were members), and was a member of the European Union until it fortunately finally left on 31 January 2020