John Gill Commentary Zechariah 12:9

"And it shall come to pass in that day, that I will seek to destroy all the nations that come against Jerusalem." — Zechariah 12:9 (ASV)

And it shall come to pass in that day
So often mentioned in this chapter; by which is meant the latter part of the Gospel dispensation, the spiritual reign of Christ:

[that] I will seek to destroy all the nations that come against
Jerusalem ;
and shall destroy them. The whole of this paragraph seems to refer to the same as in (Ezekiel 38:1-39:29) .