Why global war would rapidly disrupt merchant shipping

How badly would merchant shipping suffer if a global war began?

Very badly and very quickly, because modern supply chains are not designed to absorb major interruptions in seaborne trade.

The answer uses recent grain shortages and the Suez Canal blockage to show how even limited disturbances propagate through world markets. A major war would compound route closures, ship losses, insurance problems, and escort shortages. Food and industrial inputs would be affected long before every merchant ship was physically threatened. The central lesson is that maritime logistics are optimized for efficiency, not prolonged combat disruption.