I was told

I think it was a long, long time ago when Rome was invaded and the pope was moved to France for protection.

In the history of the Roman Catholic Church, the Avignon Papacy was the period from 1309 to 1377 during which seven popes, all French, resided in Avignon, now in France. A stronger source of influence was the move of the Roman Curia from Rome to Avignon in 1305. Following the impasse during the previous conclave and to escape from the infighting between the powerful families that produced former Popes, such as the Colonna and the Orsini, the Church looked for a safer place and found it in Avignon, which was surrounded by the lands of the papal fief of Comtat Venaissin. The Popes who lived in Avignon where;
Pope Clement V: 1305–1314
Pope John XXII: 1316–1334
Pope Benedict XII: 1334–1342
Pope Clement VI: 1342–1352
Pope Innocent VI: 1352–1362
Pope Urban V: 1362–1370
Pope Gregory XI: 1370–1378
In 1378, Gregory XI moved the papal residence back to Rome and died there. Due to a dispute over the subsequent election, a faction of cardinals set up an antipope back in Avignon:

The Pontifical States (today limited to Vatican City) once included land around Avignon (Comtat Venaissin) and a small enclave to the east. They remained part of the Pontifical States up to the French Revolution: they became part of France in 1791.