Revelation 16:10 And the fifth angel poured out his vial upon the seat of the beast; and his kingdom was full of darkness; and they gnawed their tongues for pain,
11 And blasphemed the God of heaven because of their pains and their sores, and repented not of their deeds.
Now the fifth angel comes and pour out his vial of darkness on the seat of the beast, the seat being the whole world because he is in charge of it. This darkness brings a bit relief to the people who have faced the previous vials but it also makes them realize the pain they are in caused by these plagues. The pain is so great it cause them to gnaw their tongues. They also continue to blaspheme God because they know these plagues come from Him because the beast can do nothing to stop them. They could ask God for mercy but they do not because their hearts have been hardened. They continue on sinning as they have even though they are in such pain and have been through so much. Does this not sound like people today? But today they still have a good chance of finding Jesus with the help of the Holy spirit, so why wait?