Isaiah 36:10
And am I now come up without the LORD against this land to destroy it? the LORD said unto me, Go up against this land, and destroy it. And am I now come up without the LORD against this land to destroy it? the LORD said unto me, Go up against this land, and destroy it.
Isaiah 36:10 belongs to the history of Sennacherib's Assyrian campaign and invasion against Judah during Hezekiah's reign, as part of the larger story of Assyria's advance and God's deliverance of the land. That history includes the siege of Lachish and the threat against Jerusalem. The word destroy in the verse means laying waste and making a land desolate, rather than specifically meaning to kill its people.
The speaker is Rabshakeh the commander speaking for King Sennacherib, claiming that the LORD had sent him against Judah to destroy it and presenting the invasion as carrying out God's command. That claim was used to intimidate Jerusalem and to undermine trust in Hezekiah's promise of deliverance.
Sennacherib is presented in the account as self-confident and blasphemous toward the God of Hezekiah. His words formed part of Sennacherib's challenge to the God of Jerusalem, whom he wrongly treated as no more able to save than the idols of the nations. The ensuing deliverance showed that the LORD, not Assyria's king or his supposed divine commission, had power over Jerusalem's fate. The biblical history of that campaign is confirmed by inscriptions found among the ruins of Nineveh.