Actually, I think the Traveler and speaker(weirdo) are somewhat a major cause of the problem. Since, in the main cutscene when you create a character it shows astronauts finding the Traveler hiding on Mars. It was just sitting there hiding. Then it took up with humanity gave them all these great gifts and then BAM everyone is friggin dead. You wake up as a guardian that died with no memory of what happened and the Speaker won't tell you jack. Yeah. They killed everyone. That is just what I get out of it anyway.