In the millions of years it has been populated by technological races, the galaxy has seen mighty modosophont empires rise and fall. Solar systems have been colonized and abandoned. Moons and planets have been converted to megastructures. Postsapient civilisations have flowered in exotic ways and then burnt themselves out. Weakly godlike transingulatans have come and gone. Newer civilisations have been built over the ruins and rubble of earlier civilizations.
In the oscillating galactic ecology the cycle of boom and bust first favours one type of civilisation, than another. Resource-hungry transingularitan expansions fill the galaxy with computronium structures, annihilating lesser civilisations, before themselves collapsing though resource depletion, destroying each other, or transcending into other universes . These periods of transingularitan dominance are called Interregnums or Oppressions by terragen modosophonts
With the disappearance of transingularitans, lesser, lower toposophic, more weedy and opportunist races are able to emerge and rapidly (relative to galactic time) establish their own empires, before being again pushed aside or consumed by the next generation of postsophonts and transingularitans. These periods of weedy dominance are called Imperiums or Occupations.
(more to be added)