Isaiah 7:1
And it came to pass in the days of Ahaz the son of Jotham, the son of Uzziah, king of Judah, that Rezin the king of Syria, and Pekah the son of Remaliah, king of Israel, went up toward Jerusalem to war against it, but could not prevail against it.
The danger to Judah named here fell within the time of Isaiah's work as a prophet, when the southern kingdom stood in grave danger. The kings of Syria and of northern Israel combined their armies to invade Judah and marched up toward Jerusalem to wage war against it. Their assault belonged to a period of severe peril for the southern kingdom, coming as part of threats already gathering against it.
At that same time the forces of Assyria were also about to spread through the land of Judah. Jerusalem itself was afterward to face siege. The chapter holding this account is to be read together with chapter 6 as a call to cease backsliding, to amend ways and doings, to obey God's voice, and to come to the waters to live under the everlasting covenant.