Or rather, ah, homunculifications? You see, Fullmetal Alchemist is set in a fantasy world ruled by alchemy, typically by official State Alchemists who automatically earn the rank of major in military forces. Alchemy is capable of producing almost anything through Transmutation Circles, although it is governed by the Law of Equivalent Exchange — in which you have to give up something equivalent in exchange for what you want. That includes the two protagonist brothers of the series, who attempted to use alchemy to resurrect their mother — literally costing an arm and leg for the one and his whole body for the other. He gets better — his brother sacrificed his arm to restore his soul to a suit of armor. That includes the main antagonistic force in the series, the homunculi created from and named for the Seven Deadly Sins by the primary antagonist of the series known as Father.