Considering that I'm pretty sure the population of Skyrim as depicted in the game is roughly a few hundred people, the Stormcloaks would be gone in a few weeks, but apparently there's an entire empire full of soldiers south of Skyrim. This suggests that not only are the Imperials a puppet government to the elves as the story points out, but they're also guilty of gross incompetence on the part of not being able to defeat the Stormcloaks. Therefore, with there being dragons everywhere and bandits hiding in every crevice, cave, shack, and outhouse, I'm pretty sure the Stormcloaks become the only reasonable choice.