I saw this movie a while back I don't remember how it starts but from where I remember watching it from it may have not been too far from the start.
Apparently Earth has been conquered by some alien empire or something and humanity are basically cavemen being used as slaves. from where I remember the main antagonist alien is seen taking one of the slaves to a room where a machine is used on him to make him smart, this is apparently a big no no so the main antagonist and his side kick have to keep it quite. The idea was that by making one of the slaves smart it could increase the work output of the others. Apparently the antagonist is using the slaves on Earth to gather gold bullion which is apparently still very valuable to the aliens but he's doing it illegally (not the salve labor, that's apparently ok).
The protagonist who had the machine used on him becomes the go between the slaves and the aliens and begins teaching the other slaves. I remember him teaching them mathematics and I remember him saying that it was universally accepted (I think he may have been referring to algebra or trigonometry). At some point he becomes aware that they are slaves and organizes a plan to free not only his fellow slaves but the Earth.
Some escape and find an old museum which has old flight simulators and showing that humanity wasn't always a slave race and that it may have been modern times in which Earth was invaded (i.e. no lasers or starships). I think they also find Fort Knox as there is a huge collection of gold bricks and weapons.
The protagonist comes up with a plan to destroy some sort of teleporter the aliens use to transport stuff to and from Earth however that alone wont be enough as they could fight back which will be bad for humanity still being undeveloped. So the plan also includes using the teleporter before destroying to to transport and detonate a nuclear warhead on the alien home world which apparently cripples any attempt to immediately send a fleet but also as a show of strength.
After executing their plan main antagonist is captured by the humans and as an insult is locked in a cage surrounded by the gold he sought. If I recall correctly the place is set to detonate as to destroy the precocious gold and that will be used against the aliens should they mobilize a fleet in the future (i.e. attack us and we destroy Earth's supply of gold).
The antagonist's side kick for some reason I remember as a big black man who the antagonist had removed his hand at some point and also apparently the antagonist was cruel to him. After the antagonist is locked up he is trying to appeal to his sidekick's loyalty however the sidekick takes the human's side, I'm also getting an image that apart from treating him kindly the sidekick's missing hand was restored.