The Assyrian Empire had been a world power for about 150 years when Isaiah began ministering, its capital was Nineveh. It was about 840 B.C. that king Jehu had begun to pay tribute to Assyria. Isaiah was still very young when the Assyrian king, Tiglath-Pilesar III, took the 10 northern tribes of Israel into captivity in 734 B.C. About 13 years later in 722 B.C. the capital city of Israel, Samaria, fell to the Assyrians and Israel was led away into captivity. Then the Assyrian army came into the Southern Kingdom of Judah and destroyed 46 walled cities, and took over 200,000 Hebrew captives away to Assyria. King Sennacherib of Assyria mocked God and in 701 B.C. when he attacked the walls of Jerusalem the Lord smote 185,000 Assyrian soldiers and Sennacherib went back to Nineveh the same way in which he came. This was all predicted by the prophet Isaiah who was an eyewitness to the destruction of the entire promised land of Israel by the Assyrians, except Jerusalem. The Assyrian Empire was finally suddenly and completely destroyed by the Babylonians in 612 B.C. by the Babylonians and the Medes, yet the real devastation was not by human hands.
The Biblical account is confirmed and illustrated by the inscriptions of Assyrian kings such as Tiglath-pilesar III, Sargon II, Sennacherib, and Esarhaddon.