Ok I have been watching some videos on the lore and history of the Destiny universe. It says that after the Traveler came there was the Golden Age. Then the Darkness found the Traveler and they had a battle. It seems like it was meta physical battle. Now did mankind just go crazy and most of them died? There did not seem to be Fallen, Taken, Vex, or Hive in Sol till after the battle that wiped out most of mankind. The video says they drown in darkness.