Board Thread:General Discussion/@comment-26006155-20190820122909/@comment-26907577-20190826114454

They can't replicate Gaster's tech after Gaster dies. The tech outside the CORE stays in time with humanity, and therefore dependent on humanity. The CORE tech (and video camera) is Gaster's, the rest is humanity's and is slowly built up until Frisk falls.

Timeline v2: 6-8 is still a little shaky depending on what led the monsters to re-expand.
 * 1)  War of Humans and Monsters in medieval time
 * 2)  Several years pass
 * 3)  Gaster shows up.
 * 4) Asriel is born
 * 5) About 10 years
 * 6) Monsterkind expands outward and builds the CORE.
 * 7) 201X
 * 8) Chara falls
 * 9) Gaster is shattered.
 * 10) Buttercup incident
 * 11) Many, many years, during which monster technology in the CORE is stagnant at Gaster's level and slowly increases in ability in the rest of the Underground. Six humans fall.
 * 12) Modern times. CORE is still futuristic, most of the Underground is modern.
 * 13) Frisk falls