The Marshall Islands consist of 29 atolls and 5 isolated islands organized into two parallel chains. The Ratak Chain runs northeast and the Ralik Chain runs southwest across approximately 750,000 square miles of ocean. Total land area measures 70 square miles. Majuro Atoll holds the capital and roughly half the national population of 42,000. Kwajalein Atoll contains the world's largest lagoon at 839 square miles of enclosed water. Twenty-four of the 29 atolls support permanent human settlement.
The indigenous population speaks Marshallese, an Austronesian language with two principal dialect groups corresponding to the two atoll chains. The Ratak dialect dominates the eastern atolls and the Ralik dialect the western atolls. Ebon Atoll in the far south has distinct phonological features that some linguists classify as a third dialect. English serves as the co-official language and medium of instruction from grade school forward. Census data indicate 90 percent of residents identify as ethnically Marshallese. No other ethnic group exceeds 3 percent of the population.
Spanish explorer Alonso de Salazar sighted the southern atolls in 1526. Spain claimed the islands but never established permanent infrastructure or administration. British captain John Marshall sailed through the archipelago in 1788, and European cartographers subsequently applied his name. Spain sold the islands to Germany in 1885 for 4.5 million marks. German administrators established copra plantations and a trading network centered on Jaluit Atoll. Japanese forces occupied the islands in 1914 during World War I. The League of Nations formalized the South Seas Mandate to Japan in 1920.
Japan militarized the atolls during the 1930s. Kwajalein and other central atolls received naval facilities, airstrips, and fortifications. United States forces captured Kwajalein and Enewetak in February 1944 and Majuro without opposition. The Battle of Kwajalein killed approximately 7,800 Japanese and 370 American personnel. The United States isolated Japanese garrisons on bypassed atolls for the remainder of the war. Mili Atoll remained under Japanese control until surrender in August 1945.
The United States Navy administered the Marshall Islands from 1945 until 1947. The United Nations Security Council established the Trust Territory of the Pacific Islands in 1947 with the United States as administering authority. The trust territory encompassed the Marshall Islands, Caroline Islands, and Mariana Islands. The arrangement explicitly permitted military use. The United States selected Bikini Atoll and Enewetak Atoll as nuclear test sites in 1946.
The United States relocated 167 Bikini residents to Rongerik Atoll in March 1946. Operation Crossroads detonated two atomic bombs at Bikini lagoon in July 1946. Test Able exploded in air at 520 feet altitude. Test Baker detonated underwater at 90 feet depth and produced the first observed base surge and long-term radiological contamination of naval vessels. The United States conducted 67 nuclear tests in the Marshall Islands between 1946 and 1958. Bikini Atoll received 23 detonations. Enewetak Atoll received 43 detonations. Castle Bravo at Bikini on March 1, 1954 yielded 15 megatons, the largest nuclear device the United States has detonated. Unexpected wind patterns carried fallout over Rongelap Atoll and Utirik Atoll. The United States evacuated 236 Marshallese from Rongelap, Ailinginae, and Rongerik three days after Castle Bravo. Twenty-three Japanese fishermen on the tuna boat Daigo Fukuryu Maru received radiation exposure east of Bikini. Radio operator Aikichi Kuboyama died in Tokyo on September 23, 1954.
The Marshall Islands formed a constitutional government within the trust territory in 1979. Amata Kabua, a paramount chief from Majuro, became the first president. The Compact of Free Association with the United States took effect in 1986. The compact grants the United States defense authority and military base rights. The United States operates the Ronald Reagan Ballistic Missile Defense Test Site on Kwajalein Atoll. The compact provides Marshall Islands citizens unrestricted entry to the United States for residence, education, and employment. Approximately 30,000 Marshallese live in the United States, with concentrations in Arkansas, Hawaii, and Washington. The United Nations admitted the Marshall Islands to membership in 1991. The Compact of Free Association underwent amendment in 2003 with annual financial assistance extending through 2023 and economic provisions through 2086.