Short answers, pulled from the story.
Radiocarbon dating suggests that Bikini Atoll may have been inhabited as early as 1200 BCE. Archaeological digs on other atolls found evidence of human habitation around the 1st century CE at the village of Laura on Majuro and on Kwajalein Atoll.
Spanish explorer Alonso de Salazar was the first European to sight the Marshall Islands on the 21st of August 1526 while commanding the Santa Maria de la Victoria. The expedition of Álvaro de Saavedra Cerón landed on an uninhabited island possibly in Ailinginae Atoll on the 2nd of January 1528 where they named the islands Los Pintados or the Painted Ones.
From 1946 to 1958, it served as the Pacific Proving Grounds for the United States and was the site of 67 nuclear tests on various atolls. Operation Crossroads atomic bomb testing began in 1946 on Bikini Atoll after some of the residents were forcibly evacuated and the world's first hydrogen bomb Mike was tested at the Enewetak atoll on November 1 local date in 1952.
On the 1st of May 1979, in recognition of the evolving political status of the Marshall Islands, the United States recognized the constitution of the Marshall Islands and the establishment of the Government of the Republic of the Marshall Islands. Trusteeship was ended under United Nations Security Council Resolution 683 of the 22nd of December 1990.
The average altitude above sea level for the entire country is less than two meters which creates a high risk of permanent flooding when sea levels rise by one meter. The sea around the Pacific islands has risen four millimeters a year since 1993 which is more than twice the worldwide average rate.