The "Discovery" episode "That Hope Is You, Part 1" introduced The Burn, a cataclysmic event which happened in the 31st century. Dilithium, the power source of all starships, suddenly went inert, causing any starship with an active warp core to overload and explode. The Federation could not determine the cause of The Burn, nor predict if it would happen again. Afterwards, countless worlds seceded or could not be contacted for various reasons. Subsequently, the amount of Federation member worlds shrank from 350 at its peak to just 38. The ongoing plot thread of "Discovery"'s third season is to determine what caused The Burn and possibly restore the Federation to its former glory.