Craftsmen of the Gwaith-i-Mírdain seize power in Eregion
Event Type: Political
Age: 2nd Age - Pre-Rings
This event is not mentioned at all in The Silmarillion, only in Unfinished Tales.
"Before long Sauron had the Gwaith-i-Mírdain under his influence, for at first they had great profit from his instruction in secret matters of their craft. So great became his hold on the Mírdain that at length he persuaded them to revolt against Galadriel and Celeborn and to seize power in Eregion; and that was at some time between 1350 and 1400 of the Second Age."
Unfinished Tales, Part 2, Ch IV, The History of Galadriel and Celeborn