I suppose anything is possible...but ground units are needed to control a populous. If some territory needs to be captured or liberated...then something needs to be on the ground to HOLD it and take control of the local populous...and stifle whatever is the local enemy force. I guess you could talk about robots WAY WAY in the future...but as long as humans are making war...war is about land...something needs to control that land...airplanes can't capture land...a tank can't...people not technology countrol countries.