Adam Clarke on Judges 3:30

The land had rest fourscore years - This is usually reckoned from the deliverance under Othniel, that being a term from which they dated every transaction, as in other cases they dated from the exodus, from the building of Solomon's temple, etc., and as other nations did from particular events: the Romans, from the building of the city; the Mohammedans, from the Hijreh, or flight of Mohammed to Medina; the Christians, from the birth of Christ, etc., etc. But see the preface, and the different chronological schemes there mentioned.