Because being arrogant is comparable to mass genocide and making a damn road out of victims or burning a capital full of civilians or countless unprovoked aggressions or accepting some shady undead and turning a blind eye to their sick experiments on the living or using blight left, right and centre.
Oh wait…
It’s your own fault. You’re too damn tasty.
Here is how i see it happen:
Anduin manipulate the alliance into a position where the alliance will accept him as there emperor.
Removing tyrande, malfurion, jarod and miave from the playing board(aka gets them killed)
No longer needed to pretend to value the opinions of his allies anduin starts the war of unification:
Many horde join either out of hope for a better future or fear of refusal.
At first things start looking up.
Life improve’s for everyone.
But then the horror becomes known.
Worship of the light is mandetory.
All other worship is outlawed.
Night elves are the first to resist but without there heroes/dimigods anduin makes an example out of them.
Ashenvale is burned to the ground and anyone within in that doesnt instant kneel before anduin gets put to the sword.
All in the name of ever lasting peace ofcourse.
As more and more race’s fall under the empire banner the domination of the humans become ever clear.
Everything will be changed to be more like the humans of stormwind.
All other cultures are destroyed.
In desperate attemp to stop anduin war of unification the race’s of the world unite against the empire.
As anduin, velen and greymane overlook the battlefield anduin comments how he will final bring ever lasting peace as the last of those who resist will die to day.
Anduin light bless powers make his troops instant heal any wound they recieve.
Just as anduin is about to achieve victory he get stab in the back by velen.
As velens hugs a dieing anduin he tells anduin that his perversion of the light can not be allowed to continue.
The buildings would be bright, shiny, light infused.
As would the armor.
The idea is that in his attempt to achieve ever lasting peace anduin goes to far.
So everything looks unatural good.
It shoud give you the kind of feeling of wrongness despite looking so perfect and good.
As if people are too afraid to step out of line.
-Arthas made a bigger road of victims
Well you allowed 
Thats alot of shade brother
Because when an alliance character become evil, he’s never supported.
While when an horde character become evil, he’s praised and helped by the horde.
Arthas is a human but not an alliance member.
I don’t remember Stormwind sending help to the scourge.
No. They are supported.
But Blizzard and its inability to drag the faction out of the cliched Hero Trope they buried them into, makes writers often whitewash Alliance characters and their actions. Even if they are using blatant double standards that have them signalling how villainous Horde members are for doing such.
Garrosh using Molten Giants was considered a war Crime. Dark Iron doing likewise in Zuldazar was swept under the rug.
Because Garrosh was using dark shamans that enslave elementals, when Dark Irons are friend with elementals 
The new theme wouldn’t have to affect existing capitals just as Garrosh theme didn’t affect TB or UC in any way (except for some NPC) and was only applied to new settlements and re-worked Orgrimmar.
If someone on Alliance would assume tyrannical rule over rest of it and send it on path of ruthless war than the theme depends on who would do it. As for capital city that would need a rework we got two/three possibilities:
Darnassus, GIlneas and Exodar (though it being part of TBC makes it problematic).
So if Tyrande was to seize control of Alliance military or at least large portion of it (all those people who are unhappy with war ending before all Horde capitals got burned) we could expect some sort of dark part of nature inspired theme. Cities and settlements with buildings made of white rock similar to Temple of the Moon in Darnassus entwined with some dark gnarled roots / trees (but not as chaotic as in emerald nightmare) and black moonwells everywhere. Oh and on that Japanese thingies at the back of the moonwell we would have heads of their enemies dandling on the wind.
Instead of regrowing Darnassus they could build new capital around World Tree in Hyjal.
If they wanted to rework Exodar than probably it would be just Lightforged theme. Just like with Vindicar where they changed from purple & silver to gold & glowing gold. And yellow crystals. Lots of em. Everywhere. Though that would make it easy to make Lightforged influence be felt in other capitals - with those banner/crystals of theirs at every main junction and their “holy” robots patrolling the streets.
If Worgens and their king would take over than they could rebuild Gilneas. Enhance their Gothic architecture with more Industrial themes - coal powered furnaces and chimneys everywhere, choking heavy air and to make them more evil gallows and slave pens - they would need slaves to work in their coal mines (both Horde and unruly Alliance) and for entertainment, think fox hunt but with sentient humanoids as foxes and bloodthirsty werewolfs as hunters.
Those elementals are described as only responding to forceful commands and enslavement. And we have a quest a few zones away where we use a Firelands fragment to subdue another Fire elemental.
So no, Dark Irons certainly weren’t friends with those elementals.
They have a history of Dark Shamanism from back in the day when they were allies with the Twilight Hammer. And everything shown so far, highlights the fact that they’ve continued with several of said practices.
The case with these elementals is just one of them. And these are literally described as the sort of beings that would NEVER obey/collaborate with a Shaman, if it’s not under direct coercion.
This is sidetracking, but the point is that there are numerous instances where characters from either side made equivalent actions, and still were treated very differently. And more often than not, the Alliance bits get washed while Blizzard focuses on how evil the Horde ones are.
And this unwillingness to create any mildly controversial event, without automatically washing it down with a justification or by ignoring its consequences, is one of the reasons as to why the Alliance as standalone faction lacks both drive, and shades in term of narrative depth.
It was a joke, hence the smiley.
Blizzard claims to write “grey morality” stories, but they hate grey morality.
We interrupt your usual fodder of “The Horde is Eeeeevil” derailing and return you to the topic at hand.
The Alliance could quite easily turn evil, however not with Anduin at the helm. He is pious, yes, but seems to have nothing of the zealot in him.
I suppose we could look at what the Horde races could -see- as ‘Evil’ in the Alliance, and consider how those traits could be exaggerated, and see what we end up with,and bear in mind this isn’t a ‘The Horde are poor oppressed good guys’ before anyone starts going “B-But the Horde made the path of glory!” or any nonsense like that, this is how the Horde could -perceive- the Alliance to be evil.
Orcs: Well to be honest, the Orcs brought it all on themselves, they are Alien invaders. Alien Invaders don’t get to whinge when the invasion doesn’t go to plan. If you had to -stretch- things, then the younger generation could see Humans as Slavers, but that is a big stretch.
Trolls: I don’t think they even have reason to view the Alliance as ‘Evil’ The Zandalari could see the Alliance as an expansionist Empire, because it takes one to know one, but that isn’t even ‘evil’ per se.
Tauren: Yeah, they have a bit more reason, the Alliance is desecrating areas of their land with Dwarven expeditions, they were building roads through Tauren territory and killing the natives in their way, (Basically going all ‘Manifest Destiny’ on the Tauren, which we know from History is pretty evil). So yeah, to make them more evil, would be to step up that Manifest Destiny side of things.
Forsaken. This one is really easy. From the Forsaken point of view, Humans desire the eradication of their entire people, refusing to accept their right to exist in their own homes even. (Anduin unfortunately reinforces this message when he talks of ‘reclaiming’ Lordaeron…Lordaeron was already in the slightly decayed hands of those it belonged to ) . The rest of the Alliance seems happy to go along with this. Genocide is Evil, ergo the Alliance are Evil in the eyes of the Forsaken.
You don’t really need to do much to reinforce the idea , to a Forsaken mindset, that the Alliance is evil, especially when it tolerates the right of its -own- Undead to exist and own things, just not Forsaken undead.
Blood Elves: I don’t think they would regard the Alliance as Evil, so much as Mercurial and dangerous. Humans sometimes come with smiles, and sometimes with a dagger in your back. The Draenei seem to have their hearts in the right place, but then every Kil’Jaeden is just a Velen who made a bad choice, and we all know the bother the Blood Elves had with Kil’Jaeden.
The Kaldorei kicked them when they were down, a neutral nation. The other Alliance races not so much. However, the Alliance does harbour the terrorist organisation called the Silver Covenant, and defends those guilty of War Crimes, including the murder and torture of civilians.
To make them more Evil in the eyes of the Blood Elves, you’d just have to ramp up the hypocrisy. Elves of all types (Night, High, Blood, Void) hate Hyprocrisy, unless it is them being hypocritical, which is of course the definition of hypocritical! Gah! Hypocrit-ception.
So step up the Alliance doing some grim stuff, then accusing the Horde of doing the same or worse. Basically ‘Whataboutism’. Step up the Hypocrisy and that would get the Blood Elves to change their opinion from the Alliance as fickle and changeable to dangerously chaotic and refusing to recognise its own flaws. It is only a short step from there, before the Alliance becomes -too- dangerous and a ‘Problem’… All Elves have a very elastic view of what evil is, so you’d need to tailor it to what effects -them-. As with most things, to an Elven mindset the world really -does- revolve around them.
Goblins: Goblins oddly, for a fairly amoral species, have the most legit reason apart from the Forsaken. The Alliance did kill a lot of innocent people, just because they didn’t want witnesses to their act of aggression in kidnapping Thrall. Innocent -Neutral- people. Innocent -Neutral- Civilian- people. Basically in what was only one of about three or four times the Alliance has been allowed to play nasty, they really pulled out the stops. There were civilians on those boats, there would have been children on those boats. Not that the Alliance commander stopped to check, he just ordered ‘No Witnesses’. As venal, mendacious and materialistic as Goblin’s crabbed, cynical souls may be, they are not literal walking dollar signs. They are actually -people- Heck, even -Gallywix- has a woman he is head over heels in love with, (Maldy, He sends her genuine gifts of love every year, she sends him letter bombs…). They’re not going to look at their family being wiped out purely in terms of lost capital.
Maybe that would be what Goblins saw as horrifying and evil about it. It forced them to take a long hard look in the mirror. To the Alliance, those Goblins weren’t ‘people’, they weren’t even ‘commodities’ things of value, they were worthless, things of no consequence.
That would be a direct perversion of the natural order to a Species where -everything- has a price, -everything- has a value.
In a twisted way, that probably is ‘evil’ to a Goblin mindset, reducing someone’s net capital worth to Zero, not even a tool or a thing, just a nothing. Just something to be erased from the vast accounting ledger of life. A mistake to be rubbed out.
Looking at it like that? Thats Thanos levels of dispassionate evil.
Lets add into the equation that the Alliance seems to have a ‘Love the Sinner, Hate the Sin’ approach to ‘evil’ powers.
Forsaken are Undead and Evil. Scourge are Undead and Evil. Horde Death Knights are Undead and Evil. Alliance Death Knights are tragically fallen heroes, working within their tormented state to do good.
The Void is a force of Evil, it is a cosmic force of Entropy and Destruction, it is the favoured tool of the Old Gods, it is a source of power so dangerous, untrustworthy and malevolent that even the Blood Elves, those very Kleptomaniac Magpies of dodgy magic ‘Noped’ the heck away from it.
But hey, its only Evil if Old Gods, Deathwing, Void Lords do it. If the Alliance do it its -fine-
It would not be an unforgivable assumption to make, on the Horde’s part right now, that the Alliance is in fact Void corrupt, or becoming such… After all, Void and Light cannot coincide, this is a known cosmic truth, and yet…and yet…Ren’dorei and Lightforged serve together.
What cankerous sickness lurks at the heart of the Human Empire?
It doesn’t need a City update. It just needs better storytelling for both factions, especially the Alliance.
In the name of the Lich King, not the Alliance.
D!ckish but still minor comparison to Horde antics.
Alliance didn’t “allowed” Lady Prestor to do anything, it was deception and swiftly dealt with when truth came out.
Scourge, again. And Cult of the Damned also includes horde races, so you’re responsible aswell by your logic.
Same as Onyxia.
We’re perfectly fine, harmless and not shady at all. I mean, have we done nilgh’ri l’ riuh’eor? Throdogoth l’ N’zoth fhtagn.
Get your facts straight first.
Yeah, Arthas was a human from Lordaeron, whereas the WoW Alliance was founded by King Varian Wrynn of Stormwind. Two completely unrelated subjects.
Ooh! Didn’t catch it I’m afraid. Sorry.
But yeah, I agree. Blizzard doesn’t often write middles.
I don’t think Blizzard needs to exaggerate anything for either side.
I think that actions by themselves speak louder, and the Alliance indeed has had several instances that could’ve made it look villanious from an Horde point of view.
The only thing Blizzards needs to do, is to stop trying to justify, ignore, or wash any mildly controversial action for the blue side.
Much like they don’t need to signal Skeletor with the Horde every time they cause Jaina to stub a toe.
You don’t have to be born a zelot, you can also become one, when betrayals and losses mount up. Apart from that there is always magic to twist people, as has been done before. Anduin is already known to listen to his magicked bones for moral guidance, not that hard to make it mislead him, and not that out of character to have him double down on a wrong idea that feels right.
Whole war between horde and aliace started bcs Medivh was too weak to resist Sargeras (or more likely he wanted more power). Medivh opened Dark portal. Than horde was corrupted by Kil’Jaeden and forced to attack SW (poor soldiers).
So 1st step to war was made by aliance by opening of Dark portal = aliance is evil/bad side from start, so why we have this topic? They are already that evil side of conflict
Btw. we do not even need to talk about slaves and camps after that
Yeah, it’s Medivh’s fault that he was possessed by the uber evil god of the cosmos. I mean, he was a fetus, he should have known better.
But thats the problem with you Alliance hypocrites :
“We were tricked by Onyxia”
“We were tricked by Deathwing at second War”
“We were tricked by Medivh it was deception”
“We didnt expect Arthas, the son of our largest kingdom King to go villain and raise us all”
But when Horde says “Sylvannas tricked us” nope, you brought it all upon yourselves. Like. . .
Thats pretty accurate.
Aliance is like - we are weak/too dumb and we always get tricked but horde is clever/strong and they should predict all situations which can happen.
But to be clear - Sylvannas did nothing wrong 