"It was then that the Earth governments began militarizing their new interstellar craft, mostly because it was seen as economically necessary. The Others, for their part, seemed to only play along, making only the very minimal of gesture that one would imagine necessary to conduct a proper war in space. They would appear suddenly, en masse, and then vanish again, without actualy doing anything, before the pan-Earth alliance could respond. This spooked the leaders so badly that more and more of Earth was poured into arming for what was considered to be the greatest threat to mankind's being. However, not one bit of it was being used. There was great millions of trained men sitting in over two hundred thousand new fighter-craft, loaded heavy with millions upon millions of dollars of advanced weaponry, ammunition, equipment, rations. None of it ever saw much actual use against the phantom threat, the Others. Total war eventually turned to total economic collapse as the burning engines of industry whimpered with strain and wheeled down, suffocating on itself and starved. Took ten years of retrospective to piece it all together, you know, for humanity to understand what happened."
"And it all starts to happen just after I got into the time machine?"
"No, of course not. I just come up with a different story as to how we achieved a near-paradise Terran civilization to every time traveler who asks."