NPR Homewold with no ground troops so no fighting when I Landed an army, this seems unnusual particularly as I am reasonably certain when I killed off their fleet I took fire from STO weapons but I did not bombard the planet to kill them, there is no dust in the atmosphere and I have had ships in the system for most of the time since the space battle so I don't think anyone else invaded and killed their army before I arrived.
Population is 1.5 billion and I created them as an NPR if that makes a difference. I think I killed some troop transports but it seems unlikely the whole planetary garrison was in the troop ships. I can't confirm that as I have not found troop transport bays in the salvage yet,
Edit Planatery population limit was 500 million so the planet is very overcrowded , could that cause the garrison to be lost to civil unrest