There are lots of non-extinction level events that could cause high-level collapse via knock on effects. E.g., long term water issues in the American west, or

There are lots of non-extinction level events that could cause high-level collapse via knock on effects. E.g., long term water issues in the American west, or if the Glen Canyon Dam were ever attacked, you would likely see the largest east ever mass migration in America away from the American Southwest in a week or two, followed by a catastrophic famine.