horn
A "horn" is the symbol of a Gentile king (Daniel 7:24); (Revelation 17:12) and the vision is of the four world empires; (Daniel 2:36-44); (Daniel 7:3-7) which have "scattered Judah, Israel, and Jerusalem" (Zechariah 1:19).
Related Commentaries of Zechariah 1:18
Zechariah 1:18
18 Then lifted I up mine eyes, and saw, and behold four horns.