In this guide, I will be explaining what few every do and what the fifth installation of The Elder Scrolls seems to waltz around. And for those of you claiming that Skyrim is its own series and The Elder Scrolls a part of it, you would actually be mistaken. The Elder Scrolls V: Skyrim is a very self-explanatory name.
The Crimes and Lies of the Stormcloaks
First off, we have some very obvious things that most Stormcloak lovers are completely OBLIVIOUS to. The fact that they are more racist than the Altmer or even the Dunmer of Morrowind. If you install the mod Gallows of Skyrim, and then visit both Windhelm and Riften you will see a most horrifying sight that will make a normal person switch sides almost instantly. Outside of Windhelm there are three people, Argonian, Dunmer, and Argonian. None of these people did anything wrong EXCEPT exist. Now let's go to Riften. Enjoyed the ride? You did? No matter. All right, Riften has: another Dunmer (this time with neither pants nor a shirt. And the ones at Windhelm only had shirts), a burglar, and a CHILD labeled thief. This in itself is evil enough, but there is more.
Now we have the lies of Ol' Frick himself. The only point I will going over here (he's too disgusting to talked about for too long), is the fact that he completely lies about his mission. He says he wants to make Skyrim its own nation, free from the rule of The Empire. You think that's good right? No, he just wants to be the reincarnation of Adolf Hitler as he reigns as High King of Skyrim while driving everyone who isn't a Nord out of Skyrim. That means that 50% of Skyrim goes missing if he becomes High King. Not a lot of people to "draft" into his "army" when a LOT of the Empire comes into Skyrim after the winter (which it actually does in the lore).
The Empire of Tamriel
When asked what they imagine when they hear the words Empire of Tamriel normally say "Roman looking soldiers that can barely fight." And while that may be true of most of Skyrim's current Imperial equipment, that is actually just because of the Province. Equipment will DRASTICALLY change depending on what province you are in. In Hammerfell, Cyrodiil, and Highrock, the Imperial soldiers actually wear a very sturdy armor that looks a lot like what a Knight would have worn about one thousand to eight hundred years ago. This armor makes the Imperial soldiers stationed there very hard to kill, and is most likely the main armor of the Imperial military. For Morrowind, a very Roman looking armor is also worn, but it also looks much colder than that of the ones in Skyrim. The armor is made to suit the needs of the province. As for training, most guards and Imperial soldiers of Skyrim are actually auxiliaries and were never given the proper training. Many of them would have been forced to fight before though which is why they can still hold their own. And then there is the fact that a massive army as been amassed outside of Skyrim by the Empire and just needs to wait for the winter storms to clear for them to be able to come into Skyrim.
And on a lesser side note, there has never (except maybe Redguard, I've never played it) been a game where you are not helping the Empire. In Arena you are saving Uriel Septim the Seventh. In Daggerfall you are going on an errand for the exact same emperor. In Morrowind you are a Blades agent and are helping to both protect the Emperor (as is the task of the Blades) and fulfilling a prophecy. And in Oblivion, you are both saving Tamriel and fulfilling Emperor Uriel Septim the Seventh's final wish. There is no reason for Bethesda to change this.