How were 185,000 Assyrian soldiers killed?

Answer: The angel of the LORD struck them

That very night the angel of the LORD struck down 185,000 men in the Assyrian camp; in the morning there were only dead bodies.

“And that very night the angel of the LORD went out and struck down 185,000 men in the camp of the Assyrians. When the people got up the next morning, there were all the dead bodies!”— 2 Kings 19:35 (BSB)