This is the first hint in this chapter that the Messiah's rule will extend to all the earth:

• He will "decide with fairness for the afflicted of the earth"
• He will "strike the earth with the rod of His mouth"

God is Judge:

7 But the Lord abides forever;
He has established His throne for judgment,
8 And He will judge the world in righteousness;
He will execute judgment for the peoples with equity.

16 The Lord has made Himself known;
He has executed judgment.
In the work of his own hands the wicked is snared. Higgaion Selah

This phrase tells us that Jesus is the Messiah:.

God declares that His Son will strike the earth with an iron rod. We see this in Psalm 2, below, and we also see it in Revelation (the New Testament). Jesus is God's Son and will judge the earth.

6 “But as for Me, I have installed My King
Upon Zion, My holy mountain.”
7 “I will surely tell of the decree of the Lord:
He said to Me, ‘You are My Son,
Today I have begotten You.
8 ‘Ask of Me, and I will surely give the nations as Your inheritance,
And the very ends of the earth as Your possession.
9 ‘You shall break them with a ROD OF IRON,
You shall shatter them like earthenware.’”

16 Therefore repent; or else I am coming to you quickly, and I will make war against them with the sword of My mouth.

15 From His mouth comes a sharp sword, so that with it He may strike down the nations, and He will rule them with a ROD OF IRON; and He treads the wine press of the fierce wrath of God, the Almighty.

In Rev. 19, it is Jesus who treads out the wine press. In Joel, it is the Lord God. In many cases, we have seen that Jesus has the same titles and the same actions as the Lord God. This makes sense. He is the Son of God, who is in the image of God.

Proclaim this among the nations: Prepare a war;
rouse the mighty men!
Let all the soldiers draw near, let them come up!
Beat your plowshares into swords And your pruning hooks into spears;
Let the weak say, "I am a mighty man."
Hasten and come, all you surrounding nations,
And gather yourselves there.
Bring down, O LORD, Your mighty ones.
Let the nations be aroused And come up to the valley of Jehoshaphat,
For there I will sit to judge All the surrounding nations.
Put in the sickle, for the harvest is ripe.
Come, tread, for the wine press is full;
The vats overflow, for their wickedness is great.
Multitudes, multitudes in the valley of decision!
For the day of the LORD is near in the valley of decision.
The sun and moon grow dark And the stars lose their brightness.
The LORD roars from Zion And utters His voice from Jerusalem,
And the heavens and the earth tremble.
But the LORD is a refuge for His people
And a stronghold to the sons of Israel.
Then you will know that I am the LORD your God,
Dwelling in Zion, My holy mountain.
So Jerusalem will be holy,
And strangers will pass through it no more.