I think you're onto something but it may not be as big as you expect it to be. Perhaps it's the manifest of all of us uniting toward one common goal. This actually proves the common theory around here that the 5 outside circles on the grid that was crafted just recently, reprsents the 5 different factions, and the major circle that eclipses all of the outer circles is actually the Last City on Earth. This "Manifest Destiny" could be that manifestation of all factions striving to save the one final city. I don't think it leads to the possibility of us having immigrated to Earth and colonized it and then started off fresh or something, I just think it's more of a push for the fact that we all have to work together on this because it's an MMO. Bungie's doing a good job pushing this MMO feel and the use of Cooperative gameplay. I don't think this clue is to point in any different direction.