Assyria is the rod of God’s judgement against Israel.  God’s providential control precedes all human free choice.  God works through human will, but is not dependent upon us to accomplish His will.  The Assyrians wanted to attack the northern kingdom, God did not coerce them, but accomplishes His predetermined purposes through their free act.  “Ah, Assyria, the rod of my anger; the staff in their hands is my fury! Against a godless nation I send him, and against the people of my wrath I command him, to take spoil and seize plunder, and to tread them down like the mire of the streets. But he does not so intend, and his heart does not so think; but it is in his heart to destroy, and to cut off nations not a few;” (Isaiah 10:5–7 ESV).
God ordains Assyria to attack Israel and Judah as His judgement upon them for their haughty, hard hearts and then He judges Assyria for their arrogant heart.  “When the Lord has finished all his work on Mount Zion and on Jerusalem, he will punish the speech of the arrogant heart of the king of Assyria and the boastful look in his eyes.” (Isaiah 10:12 ESV).  Assyria fell in 612BC.  Assyria is nothing other than a tool in the Hands of the Almighty!  “Shall the axe boast over him who hews with it, or the saw magnify itself against him who wields it? As if a rod should wield him who lifts it, or as if a staff should lift him who is not wood!” (Isaiah 10:15 ESV)