Passage: When Ahaz son of Jotham, the son of Uzziah, was king of Judah, King Rezin of Aram and Pekah son of Remaliah king of Israel marched up to fight against Jerusalem, but they could not overpower it.
Now the house of David was told, "Aram has allied itself with Ephraim"; so the hearts of Ahaz and his people were shaken, as the trees of the forest are shaken by the wind.
Journal: Isaiah 1 referenced four kings of Judah during the time of Isaiah - Uzziah, Jotham, Ahaz and Hezekiah (1:1). The time frame for Isaiah 7 is 735 B.C. Isaiah 6 informed us that King Uzziah had died (6:1). King Jotham reigned a while with his father King Uzziah and a short time after King Uzziah died (apparently about 8 years). At this point (between 735 B.C. and 732 B.C, when King Jotham died), it appears that King Ahaz and his father King Jotham are reigning together. However, it is the son, King Ahaz, that is mentioned by Isaiah in the context of Isaiah 7. King Ahaz would prove to be an apostate king and a weak ruler.
(". . . King Rezin of Aram and Pekah son of Remaliah king of Israel marched up to fight against Jerusalem . . ."; "Aram has allied itself with Ephraim . . .") "Aram" is Syria, which is a vassal state to the rising power of Assyria by this time. "Ephraim" is Israel, the northern kingdom (the division between Israel and Judah happening 200 years prior), and is becoming a vassal state to Assyria in its own right. "Jerusalem" and the "House of David" are Judah which, under the leadership of King Uzziah, had been able to defend itself against Assyria up to this point.
Syria and Israel wanted to band together to better defend itself against Assyria, and wanted Judah on board. Judah, hoping to score some points with Assyria, refused to be part of the alliance. As a result, Syria and Israel marched against Judah causing great fear in the people of Judah (". . . so the hearts of Ahaz and his people were shaken, as the trees of the forest are shaken by the wind.") Apparently, according to 2 Chronicles 28:5, about 120,000 of the men of Judah were slaughtered and about 250,000 women and children were captured, though the Syria / Israel alliance was unable to "overpower Jerusalem."