Complex sentence: IT was there that Thingol was slain by the Dwarven craftsmen of Nogrod; it was later sacked by the Sons of Feanor in pursuit of the one of the Silmarils to have left Morgoth's iron crown prior to the War of Wrath.
Split into simpler sentences: It was there that Thingol was slain by the Dwarven craftsmen of Nogrod. It was later sacked by the Sons of Feanor in pursuit of the one of the Silmarils to have left Morgoth's iron crown prior to the War of Wrath.