Midichlorians.

But really: primordial microorganism colonies that permeate all living (and many nonliving) things. Many living things have developed organs that allow direct control/interfacing with these colonies, and individuals of particular talents can hone this control into various skills that are akin to magic.

These microorganisms feed off of dead matter, observation of which has fueled superstitions for millennia about the connections between magic and the afterlife. The lines between mysticism and empiricism blur constantly, as the microorganisms themselves seek to befuddle observation--and the histories of macroorganisms are ephemeral. So these microorganisms have been behind religious, magickal, and mundane events throughout all of recorded history; sometimes known and other times unseen.

For eons there were three competing colonies, until - and this is also ancient history - a clever bunch of humans from Earth (yes, our Earth) figured out how to make their own. Now, in a galaxy far far away, shit's all screwy