What did Sastor use to lock the realm? He used the strength of his believers accumulated through the years.
This move used up much of his stored Belief Power. If not for the Ruler of Light and Darkness' orders, he definitely wouldn't do something so crazy.
He was badly injured from the final battle with the Snow Mountain Archmage Iyr and was forced to go rest in the Yan Empire. However, an Archmage's body was abnormally strong. Once hurt, it required a great amount of energy to heal.
Where did this energy come from? From the millions of believers in the Yan Empire. The Belief Power from regular believers was weak and impure. The purification process took a lot of time. Thus, to quickly replenish his power, he had to rely on the hardcore believers.
