Because of the tariffs. Countries will start developing other markets, our domestic companies will start losing business and respond by laying off workers and delaying capital expenditures which will affect other domestic business. It will keep feeding on itself.
A market correction as America flushes out stuff it doesn't need such as cheap plastic clothes hangers from China, overpriced French wine, Italian automobiles....these are peoples wants, not needs. Let the other countries try to survive without food to eat.