US recessions and bear markets happen most of the time because of mass psychosis, not because of some underlying cause. There can be a trigger, yes, but it's generally not that big of a deal. The government also plays a role in triggering these recessions, so that they can pop the bubbles before it's too late.

Yes, there can be recessions causes by world wars, worldwide droughts, pandemics and other cataclysmic events, but usually it's not the case for US.

The idea that emotional investors moving large amounts of money can single-handedly cause recessions is naive, even if it is comforting. The world has been using ZIRP for a long time. This policy has led to overinflated stock prices and a significant number of worthless loans held by regional banks, now collapsing at a rate similar to the 2008 crisis. When equity assets lose value, companies buoyed by those previous values have to reduce their spending because they would not be able to raise enough money by selling those assets, and they'd otherwise end up underwater or going bankrupt.