Antediluvian civilization refers to the people that lived in the time prior to the Great Deluge.
Evil of Mankind
According to the Bible, fallen Angels, ("the Sons of God" Gen. 6:2), had relations with human women, giving birth to giants: "the same became mighty men which were of old, men of renown."(Gen. 6:4)
Besides their powerful, super-human rulers, Antediluvian civilizations were wicked and violent (Gen. 6:5). This leads us to believe that they were not struggling to survive, rather they were basking in excess; they could afford to become corrupt because of the surplus of resources.
The legendary kingdom of Atlantis may have existed during this period.