New Defender's Study Bible Notes
9:15 a year. The demonic locusts had tortured men for only five months, but these demonic horses will ravage mankind for thirteen months, making a total of eighteen months. The previous judgments of the six seals and four trumpets will presumably take about two years, so that the events under this sixth trumpet will evidently terminate at about the midpoint of the seven-year tribulation.
9:15 third part of men. Evidently around a billion people will be slain by the Satanic army. Men could not die, though they desired to do so, under the torment of the previous scorpion-like stings; now they could hardly escape death. Already a billion people had been slain under the fourth seal judgment (Revelation 6:8), and now an equal number are killed by the Euphrates demons. All men will realize by this time that they are suffering because of their rebellion against their Creator and the One who came as their proffered Redeemer, but most will still (perhaps with a few exceptions) refuse to repent (Revelation 9:20).