The rest of mankind who were not killed by these plagues still did not repent of the work of their hands; they did not stop worshiping demons, and idols of gold, silver, bronze, stone and wood—idols that cannot see or hear or walk. Nor did they repent of their murders, their magic arts, their sexual immorality or their thefts.Revelation 9:20-21 NIV
This is a part of the sounding of the seven trumpets. The fifth trumpet unleashed devastation on the earth in the form of demon oppression. While the sixth unleashing of some form of army, either human or demonic, that would kill a third of mankind. Regardless how one views these two woes, they represent a terrible time of judgement on the peoples of earth.
But I have to wonder why? Judgement against unbelievers will last for an eternity, so why this period of time while still on earth? And I think this verse may give an answer to that question. Those not killed by the armies of the sixth trumpet did not repent. Was that the goal of this judgement, to bring people to repent and turn to God? It is possible that this time of judgement is one last opportunity for people to turn to God before it is to late. Before they enter into the final judgement and eternity.
If so, that makes this passage heartbreaking. Even after getting a taste of God’s judgement, mankind does not repent; either of the work of their hands, their false worship of created things (Rom. 1:21-23), or their other sins. Instead it is likely that they further harden their hearts. And they look for ways to overcome this judgement by human means. So like today.