To continue from last week, Sword Art Online (SAO) is an RPG-centred online game, following the basic rules of your average MMO such as World of War Craft.
As with such games, players are given the power to create characters and develop entire virtual lives within a wholly designed world with its own rules, culture and society. SAO brings a pithier plot to the table than Accel World, even though it doesn't seem like it from this description.
You have boys and girls, men, women and even children of all ages forced to partake in a game of survival for the fittest; the fun comes from seeing what they do with the newfound mortality of life in what should have been an object of enjoyment and fun - the psychological impact on minors is even more intriguing, as their previous curiosities quickly transform into their own personal hells (the suicides are far more disturbing).
The result in not unlike that which has and would happen in a society where all authoritative structures fail, anarchy arises and people are forced to find or even create a whole new way of life. New alliances are formed, broken and recreated anew just as quickly, while previously feeble forces from a time when the game was just a game morph into great powers in the form of guilds that hold the fates of the SAO population - having taken up the mantle of beating the game on behalf of everyone else, while also using their new found authority to rule the masses.
Military forces form to oppress in tandem with the scattered powers of light that will oppose them at all costs (usually scattered groups of wannabe heroes), especially in the support of players that have taken the role of by innocent by-stander, willing to settle down in their new lives, and forever let the memory of the physical world fade (basically the cowards).