After the short description of Noah (Genesis 6:9), who was blameless in his time, the book of Genesis describes the wickedness of that time:
Now the earth was corrupt in the sight of God, and the earth was filled with violence. God looked on the earth, and behold, it was corrupt; for all flesh had corrupted their way upon the earth. Then God said to Noah, "The end of all flesh has come before Me; for the earth is filled with violence because of them; and behold, I am about to destroy them with the earth. (Genesis 6:11-13)God was about to inflict judgment upon mankind. He was about to bring catastrophe upon the earth. The explanation for why such devastation was about to occur is simple: devastation was about to come upon man because the earth was filled with wickedness. In order to grasp just how great the wickedness of the pre-flood world was, all that needs to be done is to look at how the wickedness was punished.
Judgment was about to come because the earth was corrupt in the sight of God. What men see is of little importance. Doubtless, the men of Noah's day must have deluded themselves into seeing a much brighter picture of the human race: man certainly wasn't corrupt... yes... man was on the upward climb. The future looked bright. Despite a few minor moral faults, more progress would be made and the happiness of the human population would certainly increase!
But what men see matters very little compared to what God sees. God did not see man on an upward climb toward greatness. God did not see humanity advancing in a better direction. The deceitfulness and folly of sin may have convinced men to believe that God was blind; it may have convinced them to believe that God was not in control— that He was unsure of what the future might bring. But though the minds of men consistently construct new gods according to their desires, God does not change. Ultimately, it does not matter what men see, but what God sees. And what God saw was that the earth was corrupt; He saw that the earth was filled with violence.
The Pre-Flood World: Filled With Violence (Part 2) - Genesis 6:11-13
Noah: Blameless In His Time - Genesis 6:9-10
The Pre-Flood World Soon To Be Blotted Out - Genesis 6:7
Noah's Name: Its Meaning and Significance - Genesis 5:29
Who Are the Sons of God? - Genesis 6:1-4