Famine! "...A quart of wheat for a day's wages, and three quarts of barley for a day's wages, and do not damage the oil and the wine." (6:6). A normal person will work all day for just barely enough to eat! But a rich person, will pay no more for the luxuries of life.
In Zechariah 6:6 the black horses went north. Does this mean that areas north of the Middle East will suffer the most from famine? Such as Europe and Russia?