Tidal Locking plus Zombies
The Great Migration
(Also known as The Great Evacuation)
Only an estimated 3/5 of the people in the migration were able to make the journey. Power failures in stasis pods and lost starships left a large amount of the population dead or MIA. However, enough of the population were able to make the journey to colonize the planet.
While a lot of the technology was lost during the Great Migration, much of the technology was preserved by humans. Both The Foundation and knowledgeable humans in the migration were able to preserve the technology of cyber-sciences, architecture, and weaponry. These people became known as Keepers.