The seven trumpets divide into two sections. Trumpets one to four are described in 8:6-12. Then 8:13 contains an introduction to the remaining trumpet, and a lot more happens when they are blown than took place under trumpets one to four. Trumpets five, six and seven are each said to bring woe, and since trumpet seven is concerned with the Day of Judgement (11:15) we should not be surprised that it is connected to a woe.
The first four trumpets describe the outpouring of various divine judgements on the earth, sea, creatures and cosmic bodies, with each of the judgements affecting one third. Although these judgements are serious and affect a lot of people, as well as other daily circumstances, they are not yet the full judgement that will occur when the seventh trumpet is blown. So the trumpets are reminders that greater judgement is coming.
There seems to be a similarity here with the plagues that God sent on Egypt, and since they were the indicators that redemption for Israel was near, so John is being told that signs of divine judgement on the earth are indicators that eternal redemption is about to happen.
The fifth trumpet, one of the woes on humanity, is likened to a war between locusts and humans (9:1-12). The locusts describe demons, the followers of the devil; here he is called by names that mean destroyer. His army is described as travelling rapidly around the earth, inflicting damage everywhere. An unusual perspective is given here in that the targets of the demonic powers are not believers, but everyone else (9:4). So while they are opposing the church, somehow they are being destroyed because they cannot escape from the demonic onslaught.
The sixth trumpet (9:13-19) contains details similar to the fifth in that an army follows four angels who are released for a specific time in order to kill one third of mankind by various plagues. The soldiers ride on horses that have the power to poison their victims (like scorpions). This looks like another description of the demonic army. Since they are not allowed to commence their activities until God allows, we have here another reminder that he is in control of all creatures, and can use those who oppose him in the outworking of his plans.
What was the response of people to the judgements indicated by the six trumpets? John tells us that they refused to repent of their sinful actions and attitudes towards God or towards one another. Living under circumstances of divine judgement does not change the hearts of sinners. They remain opposed to God and his kingdom.
One would expect the seventh trumpet to sound next. Yet it will not come until Revelation 11:15, when it will announce the Day of Judgement. Before then, John is given more details for his readers to consider.