Telling of the same war, 2 Kings 16:5 states that Rezin and Pekah besieged Jerusalem but failed to capture it.
During the invasion, the Philistines and Edomites were taking advantage of the situation and raiding towns and villages in Judah.
Ahaz had to pay tribute to Tiglath-Pileser III with treasures from the Temple in Jerusalem and the royal treasury.
Isaiah then announces that God himself will choose the sign: A young woman shall conceive and bear a son, and shall call his name Immanuel.
Isaiah then explains that the significance of this name is that before this child can speak, Assyria will plunder both Syria and Ephraim.