Nebulos
In the Marvel G1 comic continuity, a planet of humanoids that had lived without war for thousands of years. A group of Autobots led by Fortress Maximus sought to relocate to Nebulos in order to escape their own millenia-old conflict on Cybertron, but their arrival created dissension and mistrust within the Nebulan community. The arrival of a group of Decepticons led by Scorponok soon afterward only escalated these tensions, and Nebulos' age of peace was lost as citizens binary-bonded to Transformers on both sides of the conflict to become Headmasters and Targetmasters.
Realizing the damage that was being done to Nebulos' once-peaceful culture, the Autobots abandoned the planet to join Transformers already on the planet Earth, believing (correctly) that the Decepticons would pursue them off-Nebulos.
After this the citizens of Nebulos tainted their own energy sources so as to be poisonous to any Transformers that might seek to return to their world. When Decepticons Darkwing and Dreadwind arrived soon after the departure of the other Transformers, they soon found themselves victim of this poisoning, and lay dormant for a time. They were later revived by Nebulan traitors Hi-Test and Throttle, who had stolen power-conversion plans that eventually created the Powermasters. Hi-Q, the creator of this process, eventually binary-bonded with a reborn Optimus Prime, and several of his staff joined with other Autobots, in order to combat the threat posed by Darkwing and Dreadwind. They, too, eventually left Nebulos to join the other Transformers on Earth.
In the cartoon continuity, Nebulos was a world who's inhabitants were enslaved by the Hive, a group of ten Nebulan telekinetics in robotic bodies, led by Lord Zarak, also a telekinetic, who retained his body. The populace was mainly forced to do routine farm work, watched over by the machines which the Hive controlled telepathiclaly.
In the events of Rebirth, several Transformers crash on Nebulos. A small band of Nebulan rebels capture the Autobots, believing them to be Hive machines. The Decepticons are captured by the Hive. Convincing the rebels that they are not Hive machines, the Autobots volunteer to help, offering up four of their own to serve as Headmasters, with Nebulan pilots inside their heads to control them.
Zarak demands his own Headmasters, but Cyclonus only wishes to offer up the Decepticon animals for this. The rest offer their weapons, which Zarak willingly accepts. The Autobots learn of this and adapt the new Targetmaster designs.
In the climax, Zarak rebuilds a Hive facility into the large Transformers Headmaster body Scorponok, only to be countered by Fortress Maximus, an old Hive city converted into a Headmaster body by Spike and Cerebros. Defeated, the Hive and the Decepticons fled in Scorponok.
