Alchemy is the science of understanding, decomposing, and reconstructing matter by the rules of equivalent exchange. Alchemists have a taboo, and it is human transmutation.  Two young brothers, overcome with unbearable longing for their deceased mother, loses everything when they challenged this taboo.
The older brother, Edward Elric, wears an automail and goes by the alias Fullmetal Alchemist. The younger brother, Alphonse Elric, has his soul bound to a giant suit of armor. 
The two brothers, in order to regain what they have lost, embark on a journey seeking the Philosopher's Stone. As the siblings get closer to the truth behind the Philosopher's Stone, they plunge deeper into the helix of a giant conspiracy. 
The existence of those that are not human plotting in secrecy.
The military nation of Amestris gradually starts to show its true nature.  
Endless grudge and desires for revenge of the oppressed citizens. 
The many tragedies brought forth by Alchemy. 
The tragedies dotting the world forms a line in due time, gradually roping in people, the civilians, and even nations. 
The brothers, caught between despair and hope, must keep moving forward--.