Before Crisis's story begins shortly after the ending of
the war between the Shin-Ra Electric Power Company and the
Wutai tribe, a conflict mentioned in passing during Final
Fantasy VII. With Wutai defeated and the people of the world
now dependent on their Mako Energy and materia, Shin-ra
finds itself the dominant economic, military and political
power in the world. But there are those who remain dedicated
to the destruction of Shin-Ra, chief among them being the
newly emerged insurgent movement known as "AVALANCHE".
Before Crisis focuses on this conflict between Shin-Ra and
the original AVALANCHE group, which began six years before
the events portrayed in Final Fantasy VII, and lasted up
to the time immediately preceding the events that took place
in that game. In contrast to Final Fantasy VII, which was
focused mainly on the viewpoint of the second incarnation
of AVALANCHE, Before Crisis centers around the Shin-Ra Company's
Turks, with AVALANCHE serving as the game's main enemies.
The game unfolds through a series of "episodes."
Because of the subscription-based nature of the game, the
game's story unfolded over a period of time.
( Reference: http://www.square-enix.co.jp/mobile/bcff7.html
)