Complex sentence: With the arrival of the Cataclysm, Blizzard states that the trolls would retake their old capital, The Echo Isles, therefore killing Zalazane and taking back what is rightfully theirs.
Split into simpler sentences: With the arrival of the Cataclysm, Blizzard states that the trolls will retake their old capital, The Echo Isles. Therefore killing Zalazane and taking back what is rightfully theirs.