§ Of the Fifth Battle: Nirnaeth Arnoediad The Silmarillion

In those days Maedhros son of Fëanor lifted up his heart, perceiving that Morgoth was not unassailable; for the deeds of Beren and Lúthien were sung in many songs throughout Beleriand. Yet Morgoth would destroy them all, one by one, if they could not again unite, and make new league and common council; and he began those counsels for the raising of the fortunes of the Eldar that are called the Union of Maedhros.