Destruction warlocks are the masters of chaos, which is order unrecognized by a lesser mind according to an arcane user. Order, in reality, is most commonly perceived as arcane magic. However, this does not mean order is always perceived as arcane magic in reality. This type of energy is innately volatile, and wielding it requires intense precision and concentration. Disorder, as a opposed to order, is manifested as highly destructive fel magic. This brutal and extremely addictive energy is fueled by drawing life from living beings as if it's a demonic force used by demonic spellcasters who oppose creation. However, fel magic is not shadow magic that destroys slowly over time or a shadowflame that is fueled by burning/destroying life. Additionally, fel magic is not a force that brings everything to a state of eventual oblivion. This means that destruction warlocks are not about bringing things to a state of eventual oblivion.
The chaos that destruction warlocks are the masters of exist because of the Light and Void, forces that are ultimately responsible for spellcasters who oppose the order of mages and call down fel fire as if they're arcane practitioners known as conjurers.