Why do the nations rage,
And the people plot a vain thing?
The kings of the earth set themselves,
And the rulers take counsel together,
Against the Lord and against His Anointed, saying,
“Let us break Their bonds in pieces
And cast away Their cords from us.”
He who sits in the heavens shall laugh;
The Lord shall hold them in derision.
Then He shall speak to them in His wrath,
And distress them in His deep displeasure:
“Yet I have set My King
On My holy hill of Zion.”
Onesimus Files 
The LORD and His Anointed: Do you think Israel is ever among the nations that want to “break Their bonds in pieces”? And what of Their “cords”? Was this psalm written only about nations outside Israel (as one whole)? Or was it written when there were northern and southern divisions?
Acts 4 attributes the Psalm to David, so it was written before the Judah/Israel division.
It is my understanding that when “the Nations” are mentioned in scripture it doesn’t include Israel but refers to the gentiles.
Psalm 110:1-2a
Of David. A psalm.
[Young’s Literal Translation] The affirmation of Jehovah to my Lord:
‘Sit at My right hand,
Till I make thine enemies thy footstool.’
[NIV] The LORD will extend your mighty scepter from Zion, saying, “Rule….”
Yes. That makes sense. Still, David had internal enemies. And casting away or drawing off “Their cords from us” seems to speak of the authority relationship. It looks like there are two things addressed, both the surrounding nations (as enemies) and the enemies who don’t want to recognize their own king or the LORD’s chosen representative. The bonds of Theirs (the LORD and the Annointed) cannot be broken.