For the Alliance!

Mekkatorque isn't on the list because: a) he's in a different part of the city; and b) no gnome is worth that kind of effort.

What about Vol'jin? He is the Darkspear leader. He should count too.

To be fair, they don't include the Gnome leader, High Tinkerer Mekkatorque <King of Gnomes>, in the Horde version of this quest, For the Horde!. Still, they should include both the Gnomish and Troll leaders in these achievements, if you ask me.

With the right tactics (yes, you you need them can't just go fly into say, the building Garrosh is in and pewpew without wiping.) this is quite easy to do. And after alot of fails, I managed to do 6 runs in a row without even so much as wiping in Org. My server Bladefist EU has more horde then alliance, so it does remain to be a challenge. I'll explain my way of doing For the Alliance. (Note: Wall of text inc. But it will be worth it as it is, in my opinion, the way to succes.)

First of, there is forming the full 40 man group we need, more specificly to get Garrosh down, for the other city leaders, being with 40 man is just a plus. I like to make sure I have a healthy balance of PvE'ers and PvP'ers, because you will need the PvP'ers in Orgrimmar.
Now on my server, there are alot of people that wont hesitate to relog to horde and warn them that the alliance is coming as soon as you so much as say FTA in trade. So I plan it ahead of time on the calendar for my guild on the actual day itself, I whisper members from others guild and have people invite their friends. Anything to keep it out of trade. If you do however, get told on, then make sure you tell no one the order of the citys untill the very last moment and its always handy when you have someone with a horde char that can keep an eye on their trade so if need be, you can switch it up again. People popping on- and offline in your raid group are most likely to be the traitors.

Here are some tactics for the Undercity, Silvermoon and Thunder Bluff. As Orgrimmar has a bit more, i'll do a seperate piece on that one. Keep in mind, that the players in this raid are meant to follow the leader, wich should always have a mark on themselves. If anyone is uncertain as to where to go, you can tell them to follow the marked person.

The Undercity.
Start by gathering everyone at the sewer entrance, this saves you an annoying trip with the elevators and you can just keep flying till you are in the room where Sylvanas is.
The main annoyance here are the adds, nuke all of them down, then focus Sylvanas.
She dissapears every now and then, but will re-appear fast enough. Handeling the fight shouldn't be hard if the tank(s) manage to keep aggro. Go out the same way you went in and you're all good.

Silvermoon City.
Since you cant fly here, I gather up all my people a couple of yards away from the entrance. I'll make sure that everyone is there before we do the great walk in. I made it known in a raid warning that everyone needs to move in all at once and keep running no matter what. Some people might get knocked of their mounts and slowed, but it is not worth it to stop for them and kill the guards as more will spawn. These people will make it to the boss as well, it just takes them a bit longer. The bridge you cross to get to Lor'themar Theron you'll notice that there are alot of guards there, still, keep moving. Besides your main target, there will also be 3 other high hp adds, but they don't matter much and can easily be ignored. And even though AoE in a 40 man raid group tends to make most people go down to 1fps, its the best thing to do here to handle all the guards. Once those are down, just focus Lor'themar and you should have him down very quickly, then all you need to do is either HS or run out the same way you came in.

Thunder Bluff.
This is probaly the most easy one to do, or atleast in my opinion it is. Besides a stun every now and then and loss of aggro Baine Bloodhoof can be reached easily by flying directly to the hut he is in. Gather everyone on a rock near Thunder Bluff, all fly to Baine location and let a tank aggro him and pull him out of the comforts of his hut. He'll stun the raid a few times, wich causes loss of aggro for tanks, but can easily be taken back later.

As said, Orgrimmar is the harder place of all. Garrosh Hellscream is located in the middle of the Valley Strength in between the AH and bank, wich is one of the most crowded places in Orgimmar. Here is my version of how to kill Garrosh and handle the horde that are bound to come in and kill you, not because they like Garrosh, but because they hate alliance.
To start with, I make sure everyone gathers at a place called Boulder Lode Mine in the Northern Barrens. You can camp in a small valley where you wouldn't be spotted as easily as practically standing on Garrosh' doorstep. At this point I make sure every one in the group pays attention while I tell them the following tactics. These, in order are:
- Make sure you all fly in together and stay together, even if that means slowing down a bit to ensure everyone will make it into the room in one piece.
- When you have made it into the room, the PvE'ers, including any tanks or healer will move towards the back of the room while pulling Garrosh and stay there throughout the battle.
- The PvP'ers station themselves at the entrance of the room, to make a nice distraction for the horde, while the PvE'ers work on killing Garrosh.
- When you have horde incoming, The PvP'ers are responsible for CC (ring of frost, fear, slows etc.) and do anything to stop them from entering the room.
- IF a horde does manage to push through your PvP defense and enter the room, that person has a kill priority, wich means some of your PvPers will have to peal of the main fight to get rid of the horde inside the room. If more then one get in and form a serious threat for your PvE'ers, I advice any present rogues to use smoke bomb to secure the group from ranged dps or AoE.
- In case there are barely any horde, just because it silent, or because you have managed to wipe them, the PvPers can join into the fight with Garrosh and help dps him down.

The actual fight with Garrosh isn't hard, its the horde players that make it hard. Hence these tactics I invented. I found they worked perfectly and it showed as my For the Alliance runs where a great succes.