Why does Thingol not send his forces to the Nirnaeth Arnoediad?
When the sons of Feanor learn that one of the Silmarils is in King Thingol's possession, they send a haughty message to him to return the precious jewel to them. By then, however, Thingol is beginning to desire the jewel. He feels insulted by the message, so he refuses. When they hear this, they vow to destroy Doriath when they return from the battle.