Probably best not to get hung up on specific scenarios, though if you want to explore that space, Jared Diamond, Collapse, offers a theory of civilisational col

Probably best not to get hung up on specific scenarios, though if you want to explore that space, Jared Diamond, Collapse, offers a theory of civilisational collapse and likely mechanisms based on previous history: <https://archive.org/details/jared-diamond-collapse-how-societies-choose-to-fail-or-succeed https://archive.org/details/jared-diamond-collapse-how-socie...> I could see a pathology, one more likely attacking our agricultural base than humans directly, as being one fairly likely precipitating event. A cascade failure, including supply-chain collapse and financial contagion as well as developing political dysfunction and potentially regional or global war as consequential features of a more fundamental failure, and then the problems of local self-sufficiency in a world that's grown all-but-entirely interconnected, might do it. But the question here is far more how to recover and with what knowledge than "why'd it happen in the first place". Neal Stephenson's unspecified "agent" from Seveneves is useful here. We know that something destroyed the Moon, what it was specifically isn't really of any narrative importance.