Although it isn't the most contemporary World of Warcraft expansion - that would be the still as of yet unreleased Legion - Wardlords of Draenor was the last big expansion for Azeroth, adding in the Draenor region, an alternate timeline, a war between orcs and men and plenty of new content to explore and battle through.
And now you can unlock all of that for free. All you have to do is buy World of Warcraft and set up your subscription.
Initially there was some concern among Warcraft players that they wouldn't be able to buy Draenor any more, since it disappeared from the Battle.net store. However PCG has it that that is because the game is now free for anyone - so there would be little point in buying it.
If you own WoW, you own Draenor.
Another big aspect of that is bringing back older players who may have WoW and an ongoing subscription, but haven't played in a while. Now they can come back and enjoy Draenor's features without having to put down any more money.
The only downside to this is that the level-90 boost that Blizzard doled out to buyers of the expansion early on, is not being given out any more, so if you want to hit the top level content, you'll need to get your character there yourself.
All of this is of course to help make sure there's a lot of players ready for Legion when it releases on August 30 later this year. Will you be ready?