My knowldge of Vehicle Voltron is admittedly very limited. I never got into the series at first, and by the time I was interested, I only caught a smattering of episodes. But here's what I do know.
There were three teams made up of five vehicles each that first former larger vehicles, but also could join up to form the giant robot VOLTRON. They protected the Near Universe (i.e. near to Earth) from harm while exploring for new civilizations, while the Voltron Lion Force took care of the Far Universe.
One episode talks about "the scientist that created Voltron." As Voltron appears to be a recent addition to the Near Universe, it can be guessed that the scientist probably heard the stories and legends space explorers brought back about the Lion Force Voltron and modeled his creation after those legends. Nothing is actually said to that effect, though.
Here's a "who's who" of the Vehicle Force series:
According to what I remember, Planet Drule was shaken by earthquakes and volcanic activity and doomed to extinction. The Drules were searching for a new homeworld, but didn't agree how to go about it. Hazar's father was among the people campaigning for peaceful cooperation, but there was an equally strong side (Viceroy Throk among them) who thought a new Planet Drule -- and other worlds -- should be taken by force. I believe the Emperor was feeling torn between Hazar's father and Throk and never reached a clear decision before he was no longer in power. Apparently he and Viceroy Throk fled together after confronting Hazar.
Interestingly enough, one of the greedy faction went rogue some time ago and founded his OWN empire. His name: ZARKON. Yes, Zarkon is descended from the same race as the "nemesis" of the vehicle series. This came up in one of the last episodes of Lion Force's first season.
The rest of the details are kind of foggy. Dorma I know became involved with an underground rebellion against the faction wanting conquest. Hazar was won over to his father's ideas and eventually was the one to make peaceful contact with the Voltron Force to get their help moving to a new Planet Drule.
That peace however was shortlived, because Viceroy Throk ursurps the power and decides he will conquer the Near Universe. In "Fleet of Doom," (the final Voltron Vehicle Force show, technically) Throk teams up with Zarkon to drive the Alliance out -- Throk will rule the Near Universe and Zarkon the Far. But their combined alliance fails thanks to an equal alliance of both VOLTRONS.
And that's how the Voltron Vehicle Force's saga came to an end...