Fëanor Exiled (4990 F.A.) - Though he was freed from imprisonment, Morgoth was confined to Valinor in order to remain under the watchful eye of Manwë and the other Valar.  This was not to his liking, so he schemed at how he could he could escape his confinement.  With his treacherous tongue he sowed division between the Noldor and the Valar, convincing some of the Noldor that they were also being held by the Valar against their will.

 

"Thus ere the Valar were aware, the peace of Valinor was poisoned.  The Noldor began to murmur against them, and many became filled with pride, forgetting how much of what they had and knew came to them in gift from the Valar.  Fiercest burned the new flame of desire for freedom and wider realms in the eagar heart of Fëanor, and Melkor laughed in his secrecy..." ~The Silmarillion, chap. 7 (Of the Silmarils)

 

This brought dissent between Fëanor and his brother Fingolfin.  Fingolfin sought the counsel of their father, Finwë, which Fëanor mistook as an attempt to usurp his birthright as the older sibling.

 

"Then there was great unrest in Tirion, and Finwë was troubled, and he summoned all his lords to council.  But Fingolfin hastened to his halls and stood before him, saying: 'King and father, wilt thou not restrain the pride of our brother, Curufinwë (Fëanor), who is called the Spirit of Fire, all too truly?  By what right does he speak for all our people as if he were king?...But even as Fingolfin spoke, Fëanor strode into the chamber, and he was fully armed: his high hellm upon his head, and at his side a mighty sword. 'So it is, even as I guessed,' he said.  'My half-brother would be before me with my father, in this as in all other matters.'  Then turning upon Fingolfin, he drew his sword, crying: 'Get thee gone, and take thy due place!'

 

"Now the unrest of the Noldor was not indeed hidden from the Valar, but its seed had been sown in the dark; and therefore, since Fëanor first spoke openly against them, they judged that he was the mover of discontent, being eminent in self-will and arrogance, though all the Noldor had become proud.

 

"But now the deeds of Fëanor could not be passed over, and the Valar were angered and dismayed; and he was summoned to appear before them at the gates of Valmar, to answer for all his words and deeds.  There also were summoned all others who had any part in this matter, or any knowledge of it; and Fëanor standing before Mandos in the Ring of Doom was commanded to answer all that was asked of him.  Then at last the root was laid bare, and the malice of Melkor revealed; and straightway Tulkas left the council to lay hands upon him and bring him again to judgement.  But Fëanor was not held guiltless, for he it was who had broken the peace and drawn his sword upon his kinsman..." ~The Silmarillion, chap. 7 (Of the Silmarils)

 

As punishment, Fëanor was banished from Tirion for twelve years.  But he did not go alone.  A great host of Noldor left with him, including his seven sons and even his father, Finwë, the king went with him.  And so, Fingolfin became king of Tirion.  Fëanor and his troupe traveled to the northern end of Valinor and established Formenos as their new home.  But Morgoth caught wind of the judgement and escaped capture.

 

"Now Melkor, knowing that his devices had been revealed, had hid himself and passed from place to place as a cloud to the hills, and Tulkas sought for him in vain." ~The Silmarillion, chap. 7 (Of the Silmarils)