In the 41st Millenium, Equestrians have explored the entire Galaxy, and colonized thousands of planets.
Surrounded on all sides by enemies, they were forced to give up the ways of peace, and to fight for their continued survival.

Please note that "MAREINES" is not a spelling mistake, it is a combination of the words "Mare" (Female Pony) and "Marines"

Mare + Space Marines = Space Mareines

After a party was interrupted by some drunk guards, Octavia and Vinyl scratch were nearly raped.
They join the Assassins Brotherhood to better defend themselves against this kind of incident.