département de Seine-et Oise from 1793 to 1964; in 1964 the departement of Seine-et-oise is split in 3 new departements (the creation is fully implemented in 1968). Argenteuil belongs to the département of "Val d'Oise" and the arrondissement of Pontoise (Argenteuil was formerly in the arrondissement of Versailles).
In 1966 the Arondissement of Argenteuil is created.
see link for more clarity (especially the "all dates ...." link).
France
The French belong to the country of France.
France
France
Yes!!
Yes
YES
france
France
France
They belong to Great Britain and its Commonwealth and are responsible for their defence in the event of war.
Yes, St Barts is 100% part of France