Complex sentence: During the 1960s, 1970s and earlier 1980s the hall deteriorated and by the mid 1980s, Carrick District Council broached the idea of selling City Hall for redevelopment.
Split into simpler sentences: During the 1960s, 1970s and earlier 1980s the hall deteriorated. However, by the mid 1980s, Carrick District Council broached the idea of selling City Hall for redevelopment.