Albert Barnes Commentary 2 Kings 15:16

"Then Menahem smote Tiphsah, and all that were therein, and the borders thereof, from Tirzah: because they opened not to him, therefore he smote it; and all the women therein that were with child he ripped up." — 2 Kings 15:16 (ASV)

Regarding the supposed inability of Menahem to lead an expedition to Tiphsah (Thapsacus) on the Euphrates, we should first note that such an expedition was a natural sequel to Jeroboam’s occupation of Hamath (2 Kings 14:28). Furthermore, this campaign would have been greatly facilitated by the weakness of Assyria at this time, since that empire had fallen into a state of decline around 780 B.C.