Short answers, pulled from the story.
The Marshall Islands lie in the Micronesia region of the Northwestern Pacific Ocean, west of the International Date Line and north of the equator. They consist of 29 coral atolls and five main islands plus 1,220 smaller ones, split into the Ratak chain in the east and the Ralik chain in the west.
Between 1946 and 1958 the Marshall Islands served as the Pacific Proving Grounds, where the United States conducted 67 nuclear tests on Bikini Atoll and Enewetak Atoll. The world's first hydrogen bomb, codenamed Mike, was detonated at Enewetak on the 1st of November 1952.
Castle Bravo was the test of the first deployable thermonuclear bomb, whose unforeseen reactions involving lithium-7 made it more than twice as large as predicted. The fallout spread east onto the inhabited Rongelap and Rongerik Atolls, which had not been evacuated, causing radiation burns and radioactive dusting among islanders.
The islands were named for the British sea captain John Marshall, who passed through with Thomas Gilbert in 1788. Their vessels had carried convicts in the First Fleet to Botany Bay and were en route to Guangzhou, and later navigational charts gave the islands his name.
On the 1st of May 1979 the United States recognized the constitution of the Marshall Islands and its government. The country signed a Compact of Free Association with the United States in 1986, ended trusteeship in 1990, and joined the United Nations on the 17th of September 1991.
Marshallese sailors used the stars to set their initial course, then read disruptions in ocean swells to locate low coral atolls below the horizon. They wove stick charts to map swell patterns, but used these as teaching tools studied before a voyage rather than carrying them aboard.
With few natural resources, the Marshall Islands relies on a service economy, fishing, agriculture, and United States aid. Majuro is the world's busiest tuna transshipment port, and the Marshallese ship registry was the second largest in the world by 2017, behind Panama.