This Datacron unlocks the Codex Entry - Galactic History 57: The Brotherhood's Power Grows
This datacron holds unheard of power and knowledge collected by an ancient race. You access its power and discover writings which are clearly only one small piece of a massive galactic history:
United as the Brotherhood of the Sith, Exar Kun and Ulic Qel-Droma set about gathering their strength. Exar Kun sought converts to his new Sith Order among the Jedi on Ossus, killing Master Odan-Urr to claim a powerful Sith holocron.
Focused on strategy, Ulic contacted the Mandalorians, whose leader, Mandalore, had challenged the Krath cult's rule of the Empress Teta system. Ulic defeated Mandalore in a duel, and the Mandalorians rallied under his banner.
Exar Kun also gave Ulic a terrible weapon--the Dark Reaper, which was capable of drawing out the life essence of an entire army. Ulic tested the Dark Reaper against Republic troops on Raxus Prime, killing hundreds. With the Dark Reaper, Mandalorian Crusaders, the Massassi warriors and Exar Kun's own horrific alchemical creations, the Brotherhood of the Sith was finally ready to challenge the Republic.
Coordinates: X 729 , Y 173
This Datacron is located in Gorinth Canyon of Balmorra. To get here you will first need to go to Sundari Outpost and travel a bit south (go across the bridge into Gorinth Canyon) and make your way over to the hidden path that leads to this Datacron (Screenshots 1 & 2). This Datacron is so easy it isn't even funny... The only thing that could even pose a problem is the level 34 Champion nearby but if you're high enough level you can run right by him with 0 difficulty.