Geography and chokepoints: Narrow straits and isthmuses concentrate traffic because the alternative is thousands of extra miles. The Strait of Malacca, the Strait of Hormuz, the Bab el-Mandeb, and the two great canals all owe their importance to shape rather than to anything produced there.
Wind and current systems: Before steam, the monsoon cycle and the Atlantic trade winds dictated both routes and sailing seasons.
Transport technology: Steam freed ships from wind patterns, refrigeration opened perishables to long-haul trade, and containerization collapsed transfer costs.
Canals and infrastructure: Deliberate construction can create a route where none existed, as at Suez and Panama.
Security and naval power: Routes follow waters that can be policed; piracy and conflict divert traffic.
Demand for high-value goods: Early long-distance trade carried what was worth the cost of distance.
What Route Changes Set in Motion
Falling transport costs: Each major shift — oceanic sailing, steam, canals, containers — cut the cost of distance and widened the range of goods worth trading internationally.
New patterns of specialization: Cheaper shipping lets comparative advantage operate over longer distances, since transport costs no longer swamp production cost differences.
Fragmented supply chains: Once transfer costs fell far enough, a single product could be assembled from components crossing several borders, which is the basis of modern manufacturing networks.
Rising and declining ports: Container handling required deep water and large land areas, so traffic moved away from older city-center docks toward purpose-built terminals.
Political realignment: Control of a route becomes a strategic objective in itself, as the history of Suez and Panama demonstrates repeatedly.
Chokepoints and Vulnerability
Concentration creates exposure: The efficiency of routing enormous volumes through a few narrow passages is also a structural fragility, since one obstruction affects a large share of world traffic.
Closures have precedent: The Suez Canal was closed from the 1967 war until 1975, forcing traffic around the Cape of Good Hope and contributing to the construction of much larger tankers designed for that longer route.
Physical constraints shape ship design: Lock dimensions at Panama defined the “Panamax” class for decades, and the expanded locks opened in 2016 established a larger neo-Panamax standard.
Natural limits matter: Panama’s locks depend on fresh water from its watershed, tying canal capacity to rainfall in a way a sea-level canal like Suez avoids.