That I will break - That I will break his power; that I will discomfit and destroy his army.
The Assyrian - Sennacherib (see Isaiah 10.)
In my land - That is, in the land of Canaan. This is often called his land; and this expression shows that the passage does not and cannot refer to the king of Babylon, for he was destroyed in his own city Daniel 5)
And upon my mountains - That is, upon the mountains of Palestine. The army of Sennacherib was destroyed on the mountains that were near to Jerusalem (see the notes at Isaiah 10:33-34).
Then shall his yoke - The yoke of the Assyrian (see the note at Isaiah 10:27).