What does 2 Kings 19:25 mean?

'But haven’t you heard? I planned all this long ago. I decided it from the start, and now I’m making it happen: you’re just the tool I’m using to turn strong cities into ruins.' 2 Kings 19:25 - Modern Text Bible

(God says Sennacherib’s victories were only possible because God allowed it. He’s not as powerful as he thinks.)