An Alien invasion by air and ground.
Most completely misinterpret Joel chapter 2 and Revelation chapter 9. They align Joel 2 with Armageddon and Revelation 9 with the Kings of the East. These are wrong interpretations. In fact, these chapters deal with Fallen Angels and the Demonic.
In Joel 2 we are forewarned of an invasion by air. These invaders are led by Abaddon, The Destroyer. In Revelation chapter 9, the second half, we are forewarned that a 200 million demonic army will be unleashed and gathered by 4 angels who had been imprisoned in the Euphrates River. These angels will be released, and they will gather a 200 million demonic army to invade the earth by ground with the authority to kill 1/3 of mankind with fire, smoke, and brimstone.
Read The Coming Alien Invasion and the 200 Million Resurrection of Satan's Dead - by Sherry Shriner
http://www.thewatcherfiles.com/sherry/joel.htm or http://www.sherryshriner.com/sherry/joel.htm
You can catch the radio show archives on this topic at http://www.sherrytalkradio.com/archives.htm