What could threaten maritime trade in a modern war?

Could improved submarines and limited escort numbers effectively shut down maritime trade in a modern war?

They could threaten trade, alongside mines and cheap explosive swarm craft launched from a mother ship.

A viewer asks whether small escort fleets and improved submarines could shut down maritime trade in a modern conflict. Submarines still have limited weapons and cannot use deck guns as earlier boats did. Cheap explosive swarm craft deployed from a mother ship, along with mines, provide additional scalable threats. The answer extends the video's hull-numbers argument: commerce protection must handle numerous inexpensive attack methods as well as sophisticated submarines.