Existing jet fighters are controlled by people in the craft itself. This is huge weakness because it limits their ability to change velocity (speed or direction) quickly. Normal humans tend to pass out at about 5Gs (5 times the normal gravitational force). Highly trained and fit personnel can withstand short bursts about 9Gs, but that is about the limit. Injured or unconscious people do not make good command decisions.
In principle a jet fighter should be able to handle stresses up to 15Gs and beyond.
Clearly moving the pilot out of the aircraft or doing away with the pilot altogether would be a huge advantage - not just for technical reasons, but for political reasons too (ie not having them shot down). UCAVs are designed to achieve that, and at the beginning of the 21st century, the US is developing UCAVs - the Boeing X-45A.
Unfortunately, remote control from ground-based pilots is limited in effectiveness. Firstly, high bandwidth is needed back to the control (continual radar and visual feedback), secondly this is prone to jamming, and thirdly there is a time-delay. Dog-fights are won and lost in fractions of a second - fast maneuvering ability is useless without the reflexes to match it.
Software to intelligently control these vehicles, which could make sound split-second defensive and offensive combat decisions autonomously would make these an instant success. Such software does not yet exist.
A monopoly on such software would provide global air supremacy. Previous wars have mostly been won on industrial strength. A single computer program could make that concept pretty well redundant. Is it any wonder that the US military is spending so much money researching such a thing?