Symbol of the movement of armies, when associated with blood and fire denotes God’s wrath upon people nations, or governments, using as his instruments great armies. Compare Joel 2:30, Isa. 14:31, smoke comes from the north, the movement of the armies of Assyria against Israel. See also Luke 21:20.
[For a more in-depth study on biblical symbolism see eschatology “Study Series 5b Hebraic Language Symbolism”]