World trade is a network of viable stops

Rivers and ports matter because they make bulk movement commercially worthwhile. Modern container services and earlier steamers both worked from port to port, loading and unloading mixed cargoes. Long direct passages are not automatically best because ships also need safe navigation, repair opportunities, and ports where cargo can be sold or collected. General-purpose steamers carried varied goods in adaptable holds, a flexibility that later made Britain's merchant fleet especially useful to convoy supply in both world wars. Traders choose routes that offer sufficient cargo volume and profit at several stops rather than following an immutable world map. Losing a canal therefore changes the trading network as well as the mileage of a single voyage.