Joel 3:1-2  “…When I bring back the captives of Judah and Jerusalem, I will also gather all nations, And bring them down to the Valley of Jehoshaphat; And I will enter into judgment with them there On account of My people, My heritage Israel…”
This hasn’t happened yet so it’s obviously set at the last days.  I believe this is what Jesus was referring to in Matthew 25.  “All the nations will be gathered before Him, and He will separate them one from another, as a shepherd divides his sheep from the goats.”  “Assuredly, I say to you, inasmuch as you did it to one of the least of these My brethren, you did it to Me.”  This is probably at the end of the Tribulation before the start of the Millennium, but it could also be at the end of the Millennium.  He says when the Son of Man comes which appears to be when He comes back, but there is a feeling of finality to it which may not be until after the Millennial reign.  I guess if the judgment is only on those who are there, there would be people left of the nations which would put it at the beginning of the Millennium.  Zechariah 14 says “And it shall come to pass that everyone who is left of all the nations which came against Jerusalem shall go up from year to year to worship the King, the LORD of hosts, and to keep the Feast of Tabernacles.”  Sounds like the point between the Tribulation and Millennium.  Will make sense when we get there.

2  “…They have also divided up My land”
He says My land.  God is very specific about the land of Israel.  Nations would be wise to take His promises about the land more seriously, including the US.

10-11  “Beat your plowshares into swords And your pruning hooks into spears; Let the weak say, ‘I am strong.’  Assemble and come, all you nations, And gather together all around….”
Another reference to the nations gathering at Israel for war.  Again, probably at the end of the Tribulation.  The phrase about beating plowshares and pruning hooks into weapons makes me wonder.  That is opposite of what people are told at the Millennium.  Makes an interesting cap before the final battle after the Millennium.  He mentions in verse 12 that the Lord says He will sit to judge them in the Valley of Jehoshaphat so that sounds like the Trib/Mill break.

15  “The sun and moon will grow dark, And the stars will diminish their brightness.”
More reference to the end of the Tribulation.

17  “So you shall know that I am the LORD your God, Dwelling in Zion My holy mountain.  Then Jerusalem shall be holy, And no aliens shall ever pass through her again.”
Sounds like the beginning of the Millennium.

18  “And it will come to pass in that day That the mountains shall drip with new wine, The hills shall flow with milk, And all the brooks of Judah shall be flooded with water; A fountain shall flow from the house of the LORD And water the Valley of Acacias.”
Another which sounds like the beginning of the Millennium.  With all of these mentioned, I’m pretty sure the references are to the Trib/Mill break.  Parallelism makes it difficult sometimes to be specific since it can sometimes be both, but I think this one is to the end of striving for the Israelites.

21  “For I will acquit them of the guilt of bloodshed, whom I had not acquitted; For the LORD dwells in Zion.”
Sounds like the return of the nation of Israel to God.  As a nation they will finally see that Jesus is the Christ and will come to Him as a nation in fulfillment of God’s promise to Abraham.  Each one will need to make the decision for themselves, but they will all do it, those that are left.

I hope you enjoy reading and studying His word.  May it accomplish what He desires.  Please feel free to comment or post questions.  Thanks for reading!

Scripture taken from the New King James Version®. Copyright © 1982 by Thomas Nelson. Used by permission. All rights reserved.