Answer:
   
   There were two communities in countries like Syria, Iraq, and Iran.
   The first are communities that were there since the fall of the
   Temple. In the case of Iraq's Babylonian Jewery, since the fall of the
   First Temple. These are the people who maintained the institutions
   that gave us the Talmud. For example, the acadamy of Sura, in which
   half the debates of the Talmud occured (along with
   Pupedisa/Naharda'ah, the other half) was founded in the Hasmonian
   period and was closed in 1958 CE!
   
   The other community are the exiles from Spain in 1492, who were
   largely absorbed into the older communities.
   
   Technically, Edot haMizrach refer to the former, Sepharadi -- the
   latter. Of course, the communities pretty well blended. Still, we see
   customs particular to these communities that originated in the local
   traditions rather than the Spanish ones. Including pronunciation,
   diferences in prayer texts, etc... There are far more than one or two
   differences in pronunciation, cantillation and services.
   
   The Ben Ish Hai, and later R' Ovadia Yosef, has done much to unify
   Sefaradi and Edot haMizrach practice to some fusion of Sepharadi and
   Iraqi traditions.