How might World War II change if a Panamax-scale St. Lawrence Seaway were completed by 1930?
Short answerIt would improve inland access, industrial dispersal, and transport efficiency, producing many small gains whose combined wartime effect would be substantial but hard to isolate.
NotesOpening the seaway before World War II would give ocean shipping easier access to the North American interior. Industry could spread across more locations while moving raw materials and finished goods more efficiently. No single decisive campaign follows directly from the project. Many small changes in transport and production would accumulate into a larger result that is difficult to isolate in a simple counterfactual. Infrastructure often changes war through system-wide margins rather than one dramatic event.