Of a truth, Lord, the kings of Assyria have laid waste all the nations. This was a stubborn fact, which it was impossible to deny. From the time of Asshur-izir-pal at any rate, about b.c. 880, Assyria had pursued for nearly two centuries a steady career of conquest, reducing the nations which were her neighbors, almost without exception, and gradually spreading her power from the tract immediately about Nineveh to the Persian Gulf on the south, the great plateau of Iran on the east, the Armenian Mountains (Niphates and Taurus) on the north, and on the west to Cilicia and the Mediterranean.
Her progress towards the west alone is marked in Scripture, since there alone she came in contact with God's people. Under Pul she attacked Samaria (2 Kings 15:19); under Tiglath-Pileser II. she carried off a portion of the ten tribes (2 Kings 15:29); under the same monarch she subjugated Damascus (2 Kings 16:9); under Shalmaneser she besieged (2 Kings 17:5), and under Sargon took, Samaria (2 Kings 17:6); under Sargon also she invaded Philistia and captured Ashdod (Isaiah 20:1).
Now she was bent on subduing Judaea, and so preparing the way for the reduction of Egypt. Humanly speaking, it was most unlikely that the small and weak state of Judaea would be able to resist her. But God was all-powerful, and might be pleased to cast down, as he had been pleased to exalt (Isaiah 10:5-19).
Hence Hezekiah's appeal.