The correct answer to this open question is the following.
The pharaoh of the New Kingdom who treated those he defeated with mercy was Thutmose III.
Thutmose III (1458 BCE-1425 BCE) belonged to the 18th Dynasty of Pharaohs in Egypt. He was the 6th Pharaoh of the Dynasty. He is considered a great military leader and a good and well respected Pharaoh. He was married to Queen Hatshepsut. As was said before, Thutmose III was a military leader best known for his strategy on the battlefield and he never lost a battle. He has great charisma and knew when to be benevolent. He treated those he defeated with mercy was Thutmose III.