They were set on changing God's creation. They were all of one language, of one accord. We learn from the Day of Pentecost the power of 'being of one accord.' The Lord thought to change all of that with a flood; but after the flood there continued a move to change the order of God's creation. (Today we would term it 'genetics'.) Their hearts were forever set on doing evil.
God had promised that there would not be another flood, so he set his sign - a rainbow - in the heavens. Therefore the Lord God destroyed the tower (Babel) built by giants and scrambled all the languages of the post diluvian world.
This is the last time that God has directly interfered in world politics. The scrambling of tongues made understanding across cultures difficult to impossible; the fallen angels could understand the various tongues but could only sew distrust when trying to communicate various universal ideas to humans in such confusion.
Today the enemy is working prodigiously to open a portal back to pre-Babel times. For example, they have managed to get erected a 'gold' statue of a female goddess next to Moses over the entrance of a NYC courthouse:
this leading up to the arrest of Donald Trump.
Spiritual warfare has become a central part of our age... mene mene tekel upharsin...