Andromeda is based on a story idea that Roddenberry tried twice before (years before he created Star Trek); it explores the concepts of civilization and history.
The first season opening explains it well:
The Long Night has come.
The Systems Commonwealth, the greatest civilization in history, has fallen.
But now one ship, one crew, have vowed to drive back the Night, and rekindle the light of civilization.
On the starship Andromeda, Hope lives again.
Y'see, the Commonwealth makes a peace treaty with a species called tha magog. The Nietzscheans (a genetic/cultural offshoot of humans) view this as a sign of weakness, and launch a rebellion. During the first engagement, the High Guard Glorious Heritage
-class battlecruiser Andromeda Ascendant
(Capt. Dylan Hunt, commanding) is trapped on the event horizon of a black hole.
Because of the time distortions in the gravity well, time aboard the Andromeda
slows to a stop.
300 years later, the Commonwealth is only a memory. The Nietzscheans have destroyed it, then the various Prides began feuding amongst themselves, and the magog invaded en masse, and so on and so forth.
A group of mercenary smugglers (the Eureka Maru
, under Capt. Bekka Valentine) working for a Nightsider named Gerentex manage to haul the Andromeda
out of the black hole (barely), and try to salvage her.
Now, by this time, the Andromeda
most advanced (and well-made) piece of hardware in the known worlds, so none of these grease-monkeys have seen anything like her. Also, because of the time distortion, Capt. Hunt has only experienced about two seconds while three centuries passed for everyone else.
When he realizes what happened to the Commonwealth, he sets out with his newfound "crew" to re-establish it.
There's a more detailed backstory here
, on the official site.
It's basically Medieval Europe (after Rome fell and civilization "went backwards"), but spread across more than three galaxies.