If I conquered a battlefield then moved the only unit out of it, can I play a new unit back into it from hand?

Ruling: No, you cannot play a new unit into a battlefield if you have no units there. You need to have a unit at the battlefield and be in control of it to play additional units there.

Nuances:

• Even if you previously conquered the battlefield, moving your last unit out means you can no longer play units there from hand