Despite the Lord's command that Elijah anoint Hazael to be king of Syria, for whatever reason Ben-hadad is still king for the time being. He's at war with Ahab.
During a siege of Ahab's capital of Samaria, Ben-hadad sends a messenger to tell Ahab, "Here's what's up: All your silver and gold, and your prettiest wives and children are all mine now."
Ahab, who's obviously losing, says, "Okay, you win." He probably expects Ben-hadad to make Ahab his vassal, but let him keep his family and treasure with the understanding that it all really belongs to Ben-hadad.
But Ben-hadad's like, "No, I'm gonna send my people in there so they can take anything nice they see."
So now Ahab gathers his elders, and says, "What's with Ben-hadad? I agreed to surrender, but now he literally wants all my stuff. What do I do?"
His advisors are like, "Don't do it."
So Ahab tells Ben-hadad he won't settle for worse than political subjugation.
Ben-hadad is mad. He swears to take Ahab down.
Ahab's like, "I'll believe it when I see it."
So Ben-hadad commands his huge army to go against the city.
An unknown prophet comes to Ahab and tells him that the Lord is going to help him win the battle so he'll know that he's God.
How? The young nobles of Israel will follow Ahab into battle and defeat Ben-hadad.
Ahab gathers 232 young men at the head of his army of 7,000 Israelites and attacks Ben-hadad and his generals as they're inebriating themselves under the war tents they've set up in the hills around Samaria.
Ahab's army leaves no prisoners, and Ben-hadad barely escapes on horseback.
The prophet warns Ahab that Ben-hadad will return next spring to attack once again, so he'd better strengthen his defenses.
Ben-hadad's servants tell him that Israel must worship a hill god, and that's why they were so much stronger when they fought in the hills.
They suggest that Ben-hadad fight Israel in the plains, where their god (they suppose) won't be able to help them.
So that's what they do. That spring, a huge Syrian army goes out to meet the Israelite army in the plains.
Once again, a man of God tells Ahab that the Lord will give him victory to prove that he is God—and not just of the hills.
The Israelites kill 100,000 soldiers in a single day, and the Syrians flee to a city called Aphek.
There, a wall falls down on 27,000 soldiers. Big wall.
While Ben-hadad hides in the city, his advisors suggest that he surrender. They've heard that Israelite kings are merciful.
So the advisors go and ask Ahab to spare Ben-hadad's life. Ahab says, "Of course! He's my bro. Bring him on over."
So Ahab and Ben-hadad settle their differences, make some treaties, and part ways.
The Lord wanted Ahab to kill Ben-hadad, though, so he sets up a little lesson for Ahab.
A prophet disguises himself as a wounded soldier (he even gets someone to actually wound him, after some persuasion involving a killer lion) and covers his face with a bandage over his eyes.
When Ahab comes, he tells him, "King, I was fighting in the battle, but then someone told me to guard a prisoner, and that if he got away, I'd have to pay a talent of silver or die. But I got distracted during the battle, and he got away. Can you help me out here?"
But Ahab's like, "No way. You have to pay the price."
And the prophet's like, "Ah-hah!" He takes the bandage off his eyes, and Ahab recognizes him. "You let Ben-hadad get away instead of taking care of him like the Lord wanted. Now the Lord will take your life in place of his."