If we were fluent in Japanese, this new Valkyrie of the Battlefield video would probably make a lot more sense. As it stands, we're left with looking at the game's gorgeous visuals and making lame attempts at trying to understand what's going on.
Going on just what we can see in the video, it appears that the East Europe Empire Union and the Atlantic Ocean Federal Organization are fighting over rights to mine a mineral called Ragnite. Caught in between is Gallian, a country to the west of the East European empire and possibly the source of Ragnite. It looks as if it will be up to you and your "rag tag" group of countrymen to overthrow the invaders and bring the land back to peace.