Complex sentence: A revival of interest in the flag took place in the 1960s, since when it has lost an association with separatism in the mind of the public and become a widely accepted symbol for all Brittany and Bretons.
Split into simpler sentences: A revival of interest in the flag took place in the 1960s. Since then, it has lost an association with separatism in the mind of the public and become a widely accepted symbol for all Brittany and Bretons.