Returning to Europe or to Be an International Role?---The Role Choice of the UK in the Cause of European Common Defense

European integration has developed for 60 years, which has been clearly branded with the “irreversible” mark in its process. Common defense has become the node in its in-depth development. The UK, as an important member of the European Union (the EU), has played a crucial role in the progress of the cause for the common defense. The games between them exist from the beginning to the end and are jointly promoting the common defense of the EU.