Everybody knows that the plot for any Street Fighter game is utterly absurd, but just because it's ridiculous doesn't mean that's it's not densely and unbelievably complicated, as this intricate chart shows.
Believe it or not, there are people out there coming up with story backgrounds for Street Fighter games. Each character has a backstory, which ties in with some other character's backstory, and so and so forth until there is some kind of reasonable justification for all these people in these games to suddenly find each other and duke it out for whatever reason.
But if you thought it was simple enough as "Sagat wants to beat Ryu, so they fight," oh boy, you have no idea. There are games out there with books and books full of lore, but I'm not sure if quantity necessarily trumps complexity here, at least if we're going by the diagram Capcom has prepared as a one-stop shop for Street Fighter IV plot questions. And here I thought Lost was convoluted.
EventHubs has a bigger version of the diagram, which apparently is not without some enlightening information. If you scratched your head when Guile encountered Abel and Abel remarked that he'd seen Guile's Sonic Boom before, well here's your answer: apparently Abel had been rescued by Charlie (Guile's war buddy who he's been searching for) some years ago.
And apparently the boss you fought in the game, Seth, is only one of many Seth clones, #15 to be exact, and the genetic model used to build Seth was also used to build Abel. That explains why they look alike, but I guess it also means Abel's a clone? Guess that one went right over my head.