Datblygwyd y Datganiad o Gyfeillgarwch a Chydsafiad yng nghyd-destun Datganiad Caerdydd Cynhadledd y Rhanbarthau Morol Ymylol, a lofnodwyd gan dros 20 o arweinwyr rhanbarthol ac awdurdodau lleol yr UE fis Tachwedd diwethaf, ac sy'n gosod blaenoriaethau ar gyfer cydweithio rhwng rhanbarthau'r UE yn y dyfodol ar ôl Brexit.
The Declaration of Friendship and Solidarity was developed in the context of the Conference of Peripheral Maritime Regions’ (CPMR) Cardiff Declaration which was signed by over 20 EU regional and local authority leaders last November, and sets out priorities for future co-operation between EU regions after Brexit.