Welcome everyone, I’m making this article specifically for two reasons. The first of the two is because a lot of people I speak with make comments such as “Man I can’t believe how much tanking has changed” and its inevitably returned with “Has it really changed that much?” The second person is who this article is for, as after that conversation progresses even further, its obvious a LOT of people don’t have clarity on this topic.
The second of the two reasons, is because I’m frankly getting sick of people complain about tanking changes on the WoD beta. You guys simply don’t understand the change, which is fine, and I’m sure this one article won’t change that, but at least its off my mind. So let’s begin.
Classic –
First thing to recognize about classic is that there were three specs that could even tank for any reason whatsoever. Protection Warrior, Protection Paladin, and Feral Druid. The issue however, is that only Protection Warrior had a taunt, so as a Paladin you could only ever tank something that would never need to be taunted (ie nothing.) Feral had a different issue, that being a lack of agility gear that was relevant. Pretty much all leather gear had weapon specialization on it, or things of that nature (the stat that eventually became expertise.)
Model: 
In general, the model can be summed up by one word – Threat.
You can tell that Blizzard wanted there to be more to it then that already, by giving them an ability like Shield Block, but it was simply too infrequent and not enough in a pseudo triage healing model. Shield Wall was also a 1 hour CD originally, but became 30 minutes at some point through out classic!
For five mans, your job was to lead the group, mark for CC, and threat what you could. You CC mobs mostly because its impossible to keep threat on them, but in classic it was also very dangerous to tank many, because dodge, block, and parry (combat table coverage) are not what they are today. It was very very common to take unmitigated swings.
Burning Crusade –
In TBC, they gave Paladins and druids real taunts, and real gear options to tank from level 70 normals all the way through sunwell. Each tank had its ups and downs, but many people still considered a warrior to be the only option for a raid tank, because the others still lacked definite cds and debuffs.
Its at this point that people first start recognizing the important of Thunderclap, Demo Shout, Disarm, and Shield Block.
Model: Even more surely a threat based model, especially outside of raids. 
In classic, there was very little to worry about in the way of 4-6 mob packs that weren’t just AOE trash, but TBC introduced this type of pull in a lot of its 5 mans. Historically, people remember these as a true challenge, but it lied at the heart of the tanking model, not the mechanical design. The tank simply could NOT get threat on them all unless they were a paladin with high spell power.
Towards the end of TBC we start seeing the new model surface, likely by accident.
Wrath of the Lich King –
Wrath saw the introduction (finally) of rotational defensive CDs. Divine Protection was the biggest one; the spell changed from a weaker hard bubble to a 2 minute 20 percent damage reduction and we never looked back.
Shield Block, shield wall, and last stand all became useable in rotation, and the birth of Combat Table Coverage caps (CTC) was born. With defensive stats readily selectable from gear options, the game had come a LONG way, maybe not even intentionally.
Model: 50 percent threat, 50 percent survival. 
Honestly, I struggle to believe they wanted this to go this direction this quickly, but once people saw how easy Wrath five mans were, there was no turning back. But once again, you need to understand WHY this was the case. We went from 5-7 mob packs in TBC that simply COULD not be pulled without some dedicated CC. It literally was not possible to threat them all. In wrath, these 5-7 mob packs were just more heavy damage then a 3-4 mob pack. Every tank had a viable AOE, and with the introduction of DKs, we see the first real overpowered AoE to join a tank arsenal since Paladins got sorted out in Howling Blast. Frost DK tanks simply had no concerns with threat, and thus the model was shattered.
A warrior still had to battle, but Thunderclap’s threat was dramatically increased, so if you just charged in, tclapped, and then tabbed and cleaved, you would have no concerns either. The dawn of the new age has begun!
Cataclysm –
I consider this the dim hours for Tanking. They were crossed up between what happened with the abandoned threat model, and what was emerging as an overpowered reduction model, giving way to the submodel of DPS. Cataclysm five mans were considered among the toughest, but entirely because of the incoming damage being overwhelming. CC was used to prevent a tank death, but as they settled into this model tanks started to realize that if they simply just went ham AOE, they could do more dps then the actual players…
Model: 10 percent threat, 70 percent Survival, 20 percent DPS. 
Long story short, the availability of stats like Critical strike on Plate gear since the advent of the specialization perks make warrior tanks (and others) really consider ditching conventional tanking ideas and become another DPS. If they used their rotational CDs properly, the stats on their gear became nearly irrelevant, however a full ctc capped paladin would essentially need no healing, so it was up to the raid on which direction they wanted to go. Regardless, this solidified the death of threat tanking, and would usher in the brilliance that we see in Pandaria.
Mists of Pandaria –
This is how tanking should have always been. Threat was a fun mechanic, but felt clunky. You are the tank! Keeping yourself alive should be what its all about.
With the advent of Challenge Modes, we see this model in its purest form. Every tank has an AOE stun, and between 3-5 rotational CDs with Active Mitigation tied in. A tank who can keep his active mitigation up simply can not be killed, and this allows the spec and class to be pushed to its most extreme limits. When you pull the entire room of Scholomance and see 1.5 million DPS as a protection paladin with 960k vengeance and 300k ticking hots from your own spell, you know you have broken the video game.
The active mitigation is amazing, and so is the defensive benefit of Vengeance, but the dps aspect is simply cheesy, and was far too abused in raid encounters where a tank would be the top dps by a mile. Lesson learned, let’s move on. RIP vengeance
Warlords of Draenor –
With 6.0 comes Resolve, the child of the deceased Vengeance. It is essentially the same thing, but it only effects your self preservation, and doesn’t last nearly as long. Its very akin to the DK blood shield concept, but now for all tanks.
Model: Active Mitigation 100 percent.
At least that’s how its shaping up. It has yet to be claimed how it will transpire, but the way I see it, its all about you now. There is no super hero complex where a tank with 1.5m attack power can trump 5 dps, and there is no need for silly gear choices. All secondary stats, even critical strike, give some offensive and defensive benefit, while Bonus Armor and the tertiary stats seem to be your main difference between sets.
The point of complaint is the reduction of Shield Wall type CDs from 12 seconds to 8 and a general nerf to active mitigation, but this seems neccessary to me. 12 seconds is a long time, despite it being a 3 minute CD, and hopefully wont hinder the model too much in the long run.
Metro’s Summary and Favorites –
In brief, it has come full circle. From a pure threat model to a pure survival model. It took 10 years, but I feel both have their merits. What did NOT strike me as fun was the in between years. Especially in Cataclysm, tanking just made no sense. It was basically frowned on to do something other then try to be the top DPS, and even in the one “challenging” 5 man heroics, a fury warrior was a more capable tank then a protection warrior.
My preference is the two extremes without question. Tanking MoP Challenge Modes is the most fun I’ve had in the game, and tanking Classic five mans (and TBC five mans to some degree) is just one notch lower. The threat model was simpler but still engaging. The MoP model is far more complex, but far more rewarding when you can negate the panic.
Even with the ability pruning in WoD, there is very little lost in the way of tanking. Looking forward to a new season of CMs and the culmination of 10 years of tanking work. Can’t wait!