While Judah's King Uzziah was still alive, Judah was able to ignore the crisis. Uzziah had a strong army (2 Chr 26:11-15). Overall, Uzziah was a good and effective king, and his people hoped that he could somehow save the nation from the Assyrians. When Uzziah died, however, ungodly rulers succeeded him. During this crisis of leadership, God gave Isaiah the vision that launched his ministry for the next forty years (6:1-13).
Assyria, meanwhile, pushed steadily southward along the coast of the Mediterranean, conquering one small nation after another. During this time, Judah's policy on Assyria oscillated between appeasement and confrontation. The prophet Isaiah brought a much-needed message: God is absolutely dependable, and it is utter folly to trust in anything or anyone other than God.
Unfortunately, Isaiah's central message was not always heeded. Around 734 BC, Israel formed a coalition with Syria to stand against Assyria. When King Ahaz of Judah refused to join this alliance, Israel and Syria attacked Judah in order to force Ahaz to join them. Faced with this crisis, Ahaz foolishly chose not to trust God (7:1-12). Instead, Ahaz called the Assyrians to rescue him (2 Chr 28:16-21). Although the king of Assyria did come to the rescue, defeating Syria and Israel, he also attacked Ahaz and placed a heavy burden of taxation on Judah. Just a few years later (722 BC), Assyria defeated the kingdom of Israel again and sent most of its people into exile (2 Kgs 17:5-18).
In 701 BC, during King Hezekiah's reign, Assyria again invaded Judah. This time, Judah relied on God's faithfulness, and as promised, God rescued the nation from the Assyrian army (37:21-36).
Regrettably, God's people did not remain faithful to him. As a result, God eventually allowed Judah to be overcome by Assyria's successor, Babylon (605-586 BC). What would Judah's destruction and exile to Babylon mean in terms of God's absolute reliability, which Isaiah had proclaimed? Isaiah answered this as well: God would indeed punish Judah's wickedness. He would also preserve a remnant that one day would return to the holy land. This return would not be due to any faithfulness on their part; it would be an act of God's grace.
Upon returning from exile (538 BC, see Ezra 1:1-4), the people were again tempted to wickedness, this time by the paganism that had taken root in their homeland during their absence. Isaiah showed that the gracious God who rescued them is also the holy God who demanded their obedience, righteousness, and exclusive devotion.