The Unicron Trilogy is a sub-division of the overall
Transformers franchise that refers to the following series:
The name comes from the
Transformers Generation One villain introduced in
the animated movie, which was the first time the character had been adapted for a new television series. Each series in the Unicron Trilogy dealt with the classic Transformers lore of the war between the Autobots and Decepticons, modified for a modern audience. It began with the introduction of the Mini-cons, smaller Transformers (less than human sized) that can combine with the larger robots to give them powerful upgrades. The story of their origin and the war to claim their power leads into the introduction of Unicron himself.
Energon and
Cybertron continued after Unicrons initial defeat with additional problems that arise that could lead to the destruction of Cybertron.
Cybertron the toy line (and thus the gimmicks and preliminary story) was developed by Hasbro to be a continuation of
Armada and
Energon, but when the anime,
Transformers: Galaxy Force, was developed it was made as a different continuity line altogether (direct references are made between Armada and Energon, while Cybertron is a little bit more vague about it). The English dub of Cybertron gave it stronger ties as per Hasbro's intention. After some time of contradictory statements,
Cybertron was eventually
retconned by the Japanese fiction itself.
Because
Armada is what kicked off the trilogy some people refer to it synonymously with that series.