Thou hast increased the nation; i.e. the "righteous nation" of Isaiah 26:2—not the Jewish people merely, but "the Israel of God"—who are to be "a great multitude, that no man can number, of all nations, and kindreds, and people, and tongues" (Revelation 7:9).
Thou hadst removed it. This rendering gives a very good sense. It makes the redeemed pass in thought from their present state of happiness and glory to that former time of tribulation and affliction when they were a remnant, scattered over the face of the earth (Isaiah 24:13-15), driven into its uttermost corners (Isaiah 24:16), oppressed and down-trodden by their enemies.
But it is doubtful whether the Hebrew will bear the rendering. Most modern commentators translate, "Thou hast extended far all the borders of the land," which is certainly the more natural meaning of the words.
If we accept this view, we must regard the clause as continuing the idea contained in the former part of the verse—the nation is increased in number, and its borders are advanced—it is "a multitude that no man can number," and it has no narrower limits than the "new earth," which has been given to it for its habitation (Revelation 21:1).