Fullmetal Alchemist: Brotherhood is centered mainly around the Elric brothers and their quest. However, before long, a grand conspiracy by the supervillain Father comes to light, and Edward and Alphonse need all the help they can get to save Amestris. One of their best allies is Major-General Olivier Armstrong, who knows a thing or two about survival.
Major-General Armstrong isn't quite like her musclebound brother, Major Alex Louis Armstrong. Olivier is tough but fair and subscribes to the adage "survival of the fittest," viewing it as the ultimate law of the land, alchemy or no alchemy. Her personal story helps validate this view, and Olivier soon took an active role in battling Father and his homunculus.
Olivier, Eldest Daughter Of The Armstrongs
Olivier Mira Armstrong was hardly born into obscurity. On the contrary, she climbed the ranks, not because of the prestige of her family -- the powerful Armstrong family -- but through her own incredible merits. She is the oldest of five, and all the rest looked up to Olivier growing up. She is also the highest-ranked Armstrong and the most influential, being a Major-General within the Amestris military. Throughout Fullmetal Alchemist: Brotherhood, Olivier is a character of intelligent action.
Olivier Armstrong took command of the dam-like Fort Briggs, located at the northernmost region of Amestris, right on the border with Drachma. This is hardly a quiet backwater; the Drachma border is a perilous place since the mighty nation is always looking for a chance to invade Amestris and claim territory. So, it falls to Fort Briggs to keep the border secure, and Major-General Armstrong didn't just run Briggs; she embodies it. Her iron will, watchful eyes, sharp instincts and tactical acumen all kept the border safe from the massive Drachma army, and everyone quickly learned to respect her and her ways, both friend and foe.
Olivier subscribes to the "survival of the fittest" paradigm, and she won't vainly make an exception for herself. In a dangerous and rugged place like Fort Briggs, one slip means death, and Olivier won't mourn anyone's passing. This attitude contrasts sharply with the complacent and greedy generals and other officers of Central, who are safe from all enemies and dream of immortality and endless riches. Olivier, by contrast, believes that people must earn everything that they have, including their very lives, and this will put her in direct conflict with the corrupt Central generals who are in Father's pocket.
When Olivier Waged War On Father & Central
Olivier was largely detached from the affairs of Central and the rest of the military until trouble came knocking. Not long after the Elric brothers arrived at Briggs, the homunculus Sloth showed up since his tunnel passed right under the fort. Olivier had never seen a homunculus before, but all the same, she mounted a fierce defense and temporarily defeated Sloth.
Soon after that, General Raven arrived and tried to sell Father's plan to Olivier, tempting her with the loaded promise of immortality, eternal prestige and glory in a new world of Father's making. Olivier played along while Edward and his allies listened in (as Olivier intended), and then she attacked General Raven and buried him in wet concrete. Unfortunately, the gigantic transmutation circle around Amestris was nearly complete, and even Olivier was powerless to destroy it or deal with the shadowy Pride, who resided inside the tunnel.
During the Promised Day, Olivier commanded the Briggs militia that assaulted Central, providing cover for Edward Elric, Izumi Curtis, Colonel Roy Mustang and others to deal with Father's homunculus villains elsewhere. Olivier secured a temporary victory over Central's defenders until Wrath/King Bradley arrived. She and her brother Alex fought for their lives against Sloth -- who was determined to kill them both.
Olivier fought well, despite having no alchemy, and once Izumi Curtis and her husband Sig showed up, Sloth was finally defeated for good. From that point on, Olivier did whatever she could to buy her allies more time to deal with Father, and sure enough, Edward finally finished the job. After that, it can be presumed that Olivier resumed her station at Fort Briggs, once again watching the border for Drachma incursions -- always fighting for what she believes in.