Assyrian - Sennacherib, representative of some powerful head of the ungodly in the latter ages [Horsley].
sword, not of ... mighty ... mean man - but by the unseen sword of God.
flee - Sennacherib alone fled homewards after his army had been destroyed (Isa 37:37).
young men - the flower of his army.
discomfited - rather, “shall be subject to slavery”; literally, “shall be liable to tribute,” that is, personal service (Deu 20:11; Jos 9:21) [Maurer]. Or, not so well, “shall melt away” [Rosenmuller].