(The Seven Trumpets)
Trumpets in the Bible refer most often to calling to war. They were used for signaling and alerting the troops. The trumpets of Revelation have the same purpose. They are to call the people of God to war. They signal the troops of what will happen in the future. As such, the trumpets deal with war and conquest.
The first four trumpets deal with the military defeat of Western Rome. Since Rome was "the" nation at the time John was writing Revelation, it is only logical that God will be giving us a look at what would happen to that great nation that persecuted His people. It also would be destroyed.