"...destruction and oblivion are beautiful and pure. That it is the direction in which all things must go. You can resist it and be destroyed, or aid it and be rewarded." - SargerasDestruction is the process of destroying constructs, breaking them down into the parts that they are constructed of.
Warlocks are magical practitioners who seek to understand darker, fel-based magics, including destructive spells. Warlocks who command the power of destruction favor incantations of pure chaos and aggression in battle. In this regard, they’d find a stronger kinship with fire mages than warlocks of other disciplines—if not for their propensity to make use of magic deemed detestable by all mage orders. The destruction warlock is well-versed in discharging a dizzying array of shadow, fel, fire, and chaos magics upon opponents that rattle souls and conflagrate bodies. They require little motivation for the havoc they wreak, happy to revel in the destruction they cause—thrilled at any opportunity to watch the world erupt in discord around them.
In-Game Information Edit
This tree's emphasis is to improve the Warlock's ability to do direct damage as opposed to damage over time and greatly enhances their ability to do burst damage. It mainly affects Fire spells, but is not restricted to them.
This tree provides the warlock with four spells that are exclusive to it: Chaos Bolt, Conflagrate, Shadowburn and Shadowfury. The last 3 are instant cast direct damage spells; Chaos Bolt on the other hand has a cast time, but is the single hardest hitting spell in any Warlock's arsenal. With the inclusion of Death Coil and Shadowflame, Destruction warlocks end up with five instant cast spells. This makes them quite versatile when dealing with foes.
The warlock who chooses the path of Destruction becomes an instrument of heavy artillery. Capable of dealing massive amounts of damage over a very short period of time, but sacrificing some of their survivability in the process; their role in a battle is to either stand back and help finish off enemies one at a time before they can be healed, or charge into a melee and completely disrupt a battle, usually at the expense of their own life.
Destruction is often the spec of choice for Warlocks that would rather do heavy direct damage themselves. It is often perceived as the best spec for PvP as it gives you the tools to quickly finish off a foe. However, its usefulness in arena play, especially in 2v2, is debated. Unlike the Affliction and Demonology trees, Destruction offers very little in terms of survivability or damage mitigation — two valuable assets in arena. The tree is clearly focused on damage. The introduction of resilience took quite a bit of punch out of Destruction's PvP appeal. Moreover, many of its spells have longer cast times than the DoTs of Affliction which gives opponents the opportunity to interrupt your spellcasting.
EDIT: The following is not so true with the above: Destruction spells are mana intensive so it is vital to manage mana efficiently.