Started thinking about how they were talking about the birth of alchemy. On how a man came from the east and gave them alchemy while in the east someone came from the west. Since these seem to be two different sorts of alchemy. Also Scars brother studied eastern alchemy and after he made the tattoos on his arms he commented on how something was weird about the alchemy in the country which I'm guessing is the western alchemy.
Yeah so thinking maybe those two people were Hoenhiem and Father. If Hoenhiem is the founder of eastern alchemy and Father of western alchemy it could explain the difference and why eastern still worked even though Father nullified Ed and Als alchemy. This is mostly assumed on the fact that there's a connection between the two and Envy talking about giving power. Though if that's the case I guess Father should realize why Scar and May could still use alchemy... ohh well.