fast forward 200 years
massive interstellar starships that use an improved alcubierre drive for superluminal speeds and powerful photon engines for subluminal speeds
both drives are powered by this thing
human population skyrockets due to advances in medicine, food costs, etc
planetary colonization becomes a feasible concept
fast forward 50 years
mars now has a multi-million man self sustaining colony, as does venus
carbon nanotube starship frames become feasible, meaning the overall scale can be increased
fast forward 50 years
million man colonies live inside gargantuan starships, said starships are able to consume comets and asteroids for fuel and building materials