In Isaiah 54:9-10, we're dealing with another promise to the three sons of Noah, the Animals, and their descendants:
9 “ For this is like the waters of Noah to Me; For as I have sworn That the waters of Noah would no longer cover the earth, So have I sworn That I would not be angry with you, nor rebuke you. 10 For the mountains shall depart And the hills be removed, But My kindness shall not depart from you, Nor shall My covenant of peace be removed,” Says the LORD, who has mercy on you.
Skipping Hosea 2:18 and Jeremiah 31:27-28, for brevity, let's look at the mountains departing and the hills being removed in Ezekiel 38:19-20:
19 For in My jealousy and in the fire of My wrath I have spoken: ‘Surely in that day there shall be a great earthquake in the land of Israel, 20 so that the fish of the sea, the birds of the heavens, the beasts of the field, all creeping things that creep on the earth, and all men who are on the face of the earth shall shake at My presence. The mountains shall be thrown down, the steep places shall fall, and every wall shall fall to the ground.’
If His Covenant of Peace can't be removed, why are dividing walls being removed and why is everyone shaking?
9 Then it shall be to Me a name of joy, a praise, and an honor before all nations of the earth, who shall hear all the good that I do to them; they shall fear and tremble for all the goodness and all the prosperity that I provide for it.’ (Jeremiah 33:9)
“Run, speak to this young man, saying: ‘Jerusalem shall be inhabited as towns without walls, because of the multitude of men and livestock in it. 5 For I,’ says the LORD, ‘will be a wall of fire all around her, and I will be the glory in her midst.’” (Zechariah 2:4-5)
Jeremiah 31:27-28 answers any [foreseeable] questions about the above.