It is hard to imagine an island less like Greenland than Diego Garcia, a lush coral horseshoe halfway between Africa and Indonesia.

Both lands host American military bases. But, whereas the United States has run down its Greenland garrison, it has wisely upgraded its presence in the Chagos Islands, the archipelago of which Diego Garcia is the chief island. That cluster could not be more strategically located, lying within reach of four of the seven global choke points that funnel maritime traffic: the Bab al Mandab Strait, the Strait of Hormuz, the Malacca Strait, and the Cape of Good Hope.