A lot of ink and some blood has been spilled servicing this whole "East Vs. West Beef" deal, but not too many people are aware of the roots of the whole thing. The story itself is something else.
Way, way back in the day, when hip-hop was first invented by MC Immanuel and the Furious Twelve, early beefs that arose (such as the short-lived but high-profile defection of MC Iscariot) were far-reaching in their implications, but didn't threaten the unity of the scene. It wasn't until more than almost a thousand years later that the rise to high prominence of Eastern rap-capital New Jack Constantinople led the emcees of that city to chafe under the continued supposed preeminence of Rap City Rome, the long-established capital out West. This burgeoning rivalry saw the emcees of each scene increasingly criticizing each others' styles and lyrics, often on minor pretexts.
Things came to a head when MC Curious Mike, the acknowledged patriarch of the C-Town scene, called out the imperious kingpin of Rome's feared and respected Cardinal Posse - Big Poppa Leo. Mike refused, in so many words, to acknowledge Leo's top dog status. So Leo sent a delegation after him, headed by Cardinal Humpty-Humbert. But MC Curious Mike refused to even see them for months, and when they were finally granted an audience, everybody got so mad that a furious rap battle erupted leaving no survivors.
Ever since then things have been kind of tense, between the East and the West. All over egos, pretty much.