Once you reach other star systems then you have interstellar travel, even if it takes 50 years, you have proven you can breach the gulf.

In that case you can repeat it using the resources of the next system to hop to the one after that. Might take 500 years before the next wave, might lose half of the systems to internal strife, but it only takes a couple to start growing and due to sore of light these systems would be separate civilisations.