2 Samuel 10:17
And when it was told David, he gathered all Israel together, and passed over Jordan, and came to Helam. And the Syrians set themselves in array against David, and fought with him. And when it was told David, he gathered all Israel together, and passed over Jordan, and came to Helam. And the Syrians set themselves in array against David, and fought with him.
The Ammonite-Syrian war was wholly unprovoked on David's part and sprang from jealousy of his increasing power, beginning with his message of kindly sympathy to Hanun after the death of Nahash. The march to Helam came in the second year of that war, after Joab had beaten the allied forces in the first engagement. When the king of Syria gathered an immense army and renewed the contest, David saw how much depended on the result and took the field in person, gathering all Israel together, passing over Jordan to Helam, where the Syrians set themselves in array against him and fought with him.
By God's blessing he inflicted so disastrous a defeat that the Syrians from Lebanon to the Euphrates gave up the war and became tributary to Israel. David then pushed the war against the Ammonites with vigor until their strongholds fell and the whole region came under Israel's dominion.