So this is my attempt to delineate the history of emo into a few discrete trends and geographical hubs. None of this will be all-inclusive, but should give you an basic idea of what happened when, where, and by whom. Under construction.
After Minor Threat broke up in late 1983, the vibrant DC hardcore-punk scene that exploded in 1981 seems to start to run out of steam and fresh ideas within the established DC hardcore sound. The wistful, posthumous Minor Threat 7" "Salad Days" comes out in 1984 and drives the final nail into the coffin of DC hardcore punk. Bands all over the country begin casting about for new things to do : DRI and Bad Brains start going cheeze-metal, New York bands start doing tough-guy mosh, 7Seconds goes jangly U2 alternative, etc. The prevailing change in D.C. is toward melodic rock with punk sensibilities.
1984 marks the release of Zen Arcade by Minneapolis band Hüsker Dü, documenting their new mature sound combining furious, intense vocal delivery and driving guitars with slowed-down rockish tempos and more-complex, melodic songwriting.
In spring 1984, a new band called Rites Of Spring forms from members of The Untouchables/Faith and Deadline. This band retains a punk speed and frenzy, but brings a totally new vocal approach to the mix. Singer Guy Picciotto keeps an out-of-breath punk style most of the time, at times delving into intensely personal lyrics dripping with emotion and sweat. His voice breaks down at climactic moments into a throaty, gravelly, passionate moan.
The summer of 1985 becomes known as "Revolution Summer" when a new wave of rock-tempo, melody based, sung-vocal bands forms out of the DC punk musician pool with diverse rock sounds - Three, Gray Matter, Soulside, Ignition, Marginal Man, Fire Party, Rain, Shudder to Think, etc. Few bands retain the fast hardcore punk-based sound with the new vocal approach, Dag Nasty being the notable exception.
Minor Threat's singer, Ian MacKaye's, sings for a band called Embrace (compare the band name to earlier DC bands Minor Threat, Void, and State Of Alert) whose lyrics are emotional and deeply self-questioning, but still clear and unambiguous. Musically, the group (formed mostly of ex-Faith members) writes midtempo, somewhat jangly music with a lot of pop guitar hooks. MacKaye's vocals retain his trademark bold enunciation, with only occasional sparks of emotive delivery.
These bands' sound eventually becomes known as the classic "D.C. sound." Some of it is derisively labeled "emo," as shorthand for "emotional." One account has this term first appearing in a Flipside interview with Ian MacKaye. Shortly thereafter DC bands aquire the tag "emo-core."
Slightly later (1986), some bands begin to focus on the "emo" element itself. The Hated in Annapolis (near D.C.) seem to be the first post-Rites of Spring to do this. Shortly thereafter, Moss Icon appears in in the same town. Moss Icon strips the "emo" element down to the core, and adds a great deal of intricate, arpeggiated guitar melody (by Tonie Joy, later of Born Against, Lava, Universal Order of Armageddon, etc.) with a strong focus on loud/soft dynamics. The vocals, too, break new ground by building up to actual top-of-the-lungs screaming at songs' climaxes.
Moss Icon, as a relatively well-known band that toured some, introduces the punk scene to music that has core emphasis on emotion instead of punk energy. As such, I consider them the starting point for the emo movement, not Rites of Spring as is more commonly asserted. Later emo bands draw heavily from the Moss Icon dynamics, guitar style, and vocal delivery.