Micromaster Collection was a small line of Transformers which ran from 2002 to 2004. It consisted entirely of new releases of molds originally made for Victory, Return of Convoy, and Operation Combination.
The Micromaster Collection story was told through text on the instruction booklets, and is set in the Generation One animated continuity, at some point in the late 20th century (but prior to the awakening of the Autobots and Decepticons aboard the Ark in 1984).
A group of Autobot Seiberdroids left Cybertron to search for Optimus Prime and the Matrix of Leadership. Due to an accident, a dimensional shockwave transported their ship across the galaxy, where it crash-landed on a remote planet. (A similar rift later brought the Multiforce over from another dimension.) The shockwave also caused the Seiberdroids to mutate, evolving into Micromaster Transformers; additionally, it affected some of their minds, turning those Autobots into Decepticons. Fighting broke out, with the Autobots wanting to live peacefully among the humans and the Decepticons wanting to conquer Earth and return to Cybertron.
Eventually, the Decepticons started digging at Mount St. Hilary for an unknown reason. After chasing them away, the Autobots discovered a couple of metal fragments there--one of which bore a mysterious symbol--and concluded that there had been Transformers on Earth before.
The eventual fates of the Micromasters and Multiforce are unknown, though presumably the situation was eventually resolved in such a way that none of them were still on Earth when Mount St. Hilary erupted in 1984.