We know from Rosinante that the clan of the D. are the natural enemy of "God".
Marco then said that there is some kind of God's land up on the Red Line, in which Lunarian used to live. We don't know if Marco was referring to "God's land" as Lunarian's land but seems it is implied because Marco was just seeing King in that panel.
So if the clan of the D. is "God's natural enemy" maybe they were the responsibles of erasing the Lunarians.
Just a quick theory.

Marco then said that there is some kind of God's land up on the Red Line, in which Lunarian used to live. We don't know if Marco was referring to "God's land" as Lunarian's land but seems it is implied because Marco was just seeing King in that panel.

So if the clan of the D. is "God's natural enemy" maybe they were the responsibles of erasing the Lunarians.
