The moment you get a little deeper, you notice that the military is a key part in the development of Fullmetal Alchemist. The country where the main story is set, Amestris, is ruled by a militaristic government, at the head of which Fuhrer King Bradley stands. Ever since his ascension to power 20 years ago, conflicts with other neighbour countries have been numerous.

Not only that, but the ultimate proof that something is indeed very wrong within Amestris was the Eastern Rebellion of Ishval. A disagreement of beliefs led to an unstable situation, led to to an all-out civil war. And seven years after, almost the entire Ishvalan population had been wiped out.

It's an undestandment by now that the ways and motives within the Amestris' Military are one of the most intrincate and interesting parts of Fullmetal Alchemist and a matter that is being disclosed slowly but surely along the plot. Here's a table with ranks, meanings, uniform characteristics and examples that I thought was interesting and useful enough to make:

Daisoutou		Fuhrer	King Bradley
Taishou		General	Raven
Chuujou		Lieutenant General	Grumman
Shoushou		Major General	Olivier, Hakuro
Junshou		Brigadier General	Maes Hughes (RIP)
Taisa		Colonel	Roy Mustang
Chuusa		Lieutenant Colonel	-
Shousa		Major	Alex Louis Armstrong
Taii		Captain	Fokker
Chuui		First Lieutenant	Riza Hawkeye
Shoui		Second Lieutenant	Havoc, Breda, Ross
Juni		Warrant Officer	Vato Falman
Souchou		Sergeant Major	Kain Fuery
Gunsou		Sergeant	Denny Brosh
Gochou		Corporal	-

* Scans from Book in Figure BLUE, edited by me.