Captivity of Melkor
From Tolkien Gateway
Captivity of Melkor was the term of three ages for which Melkor was held prisoner by the Valar in Valinor. At the end of the third age of his captivity, Manwë released Melkor, but he turned back to darkness, destroying the Two Trees and fleeing back to his strongholds in the north of Middle-earth with the Silmarils.
