When the Permanent Court of Arbitration in The Hague ruled in July against expansive Chinese territorial claims in the South China Sea, Beijing’s strategy to dominate its backyard appeared to be in disarray. Politicians in Washington sought vainly to hide their triumphalism.

But, in hindsight, that was the high point — or low point, depending on your perspective — in the struggle for dominance over the crucial waterway, through which about $5tn worth of seaborne trade flows each year.

Since then, the US has suffered setback after setback in its efforts to rally other countries with competing claims in the region while China has accelerated its militarisation and construction of artificial islands that give it effective control of the territory. Even some US officials privately acknowledge that China has won the battle for the South China Sea without firing a shot. In the annals of American decline, this episode will surely loom large.