Fuller's claim that Sluys was one of the Western world's most decisive battles requires a careful test. The victory prevented the immediate invasion and removed between 16,000 and 20,000 French troops, allowing the Hundred Years War to continue on terms favorable to English campaigning. An invasion would still have faced English castles, baronial retinues, professional companies, and a concentrated military system while depending on supplies from France. The war then lasted for more than a century and invasion fears returned, so the stronger test is whether Sluys changed what France and England could attempt next.
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Does Sluys qualify as a decisive battle?
The case for J. F. C. Fuller's verdict rests on the invasion stopped, the extraordinary French losses, and the campaign opportunities created for England.