Nauru was first inhabited by Micronesian and Polynesian people at least 3,000 years ago. There were traditionally 12 clans or tribes on Nauru, which are represented in the 12-pointed star in the nation's flag. Nauruans traced their descent on the female side. Naurans practiced aquaculture - they caught juvenile ibija fish, acclimatized them to fresh water, and raised them in the Buada Lagoon, providing an additional, and more reliable source of food. The other locally-grow components of their diet included coconuts and pandanus fruit. The British sea captain John Fearn, a whale hunter, became the first Westerner to visit this island in 1798, and he named it "Pleasant Island". From around 1830, Nauruans had contact with Europeans from whaling ships and traders who replenished their supplies (such as fresh water) at Nauru. Around this time, deserters from the ships began to live on the island. The islanders traded food for alcoholic palm wine and firearms. The firearms were used during the 10-year Nauruan Tribal War that began in 1878, and by 1888 had resulted in a reduction of the population of Nauru from 1400 to 900 people.

Colonial period
Nauru was annexed by Germany in 1888 and incorporated into Germany's Marshall Island Protectorate. The Germans called the island Nawodo or Onawero. The arrival of the Germans ended the war, and social changes brought about by the war established kings as rulers of the island. The most widely-known of these was King Auweyida. Christian missionaries from the Gilbert Islands arrived in 1888. The Germans ruled Nauru for almost three decades. Robert Rasch, a German Trader who married a native woman, was the first administrator, appointed in 1890.

Phosphate was discovered on Nauru in 1900 by the prospector Albert Ellis. The Pacific Phosphate Company started to exploit the reserves in 1906 by agreement with Germany. The company exported its first shipment in 1907. In 1914, following the outbreak of World War I, Nauru was captured by Australian troops. Australia, New Zealand, and the United Kingdom signed the Nauru Island Agreement in 1919, creating a board known as the British Phosphate Commission (BPC). This took over the rights to phosphate mining.[8] According to the Commonwealth Bureau of Census and Statistics (now the Australian Bureau of Statistics), "In common with other natives, the islanders are very susceptible to tuberculosis and influenza, and in 1921 an influenza epidemic caused the deaths of 230 islanders." In 1923, the League of Nations gave Australia a trustee mandate over Nauru, with the United Kingdom and New Zealand being co-trustees, also.

World War II
In 1943, the U.S. Army Air Force bombed the Japanese airstrip here, destroying about 15 enemy warplanes. On the 6th and 7th of December, 1940, the German auxiliary cruisers Komet and Orion sunk four supply ships in the vicinity of Nauru. On the next day, Komet shelled Nauru's phosphate mining areas, oil storage depots, and the shiploading cantilever. The attacks seriously disrupted phosphate supplies to Australia and New Zealand (mostly used for munition and fertilizer purposes.)

Japanese troops occupied Nauru on 26 August 1942. The Japanese troops built an airfield on Nauru which was bombed for the first time on 25 March 1943, preventing food supplies from being flown to Nauru. The Japanese deported 1,200 Nauruans to work as laborers in the Chuuk islands. Nauru, which had been bypassed and left to "wither on the vine" by American forces, was finally set free from the Japanese on 13 September 1945, when Captain Solda, the commander of all the Japanese troops on Nauru, surrendered the island to the Royal Australian Navy and Army. This surrender was accepted by the brigadier J. R. Stevenson, who represented Lieutenant General Sturdee, the commander of the First Australian Army, on board the warship HMAS Diamantina Arrangements were made to repatriate from Chuuk the 737 Nauruans who survived Japanese captivity there. They were returned to Nauru by the BPC ship Trienza in January 1946. In 1947, a trusteeship was established by the United Nations, and Australia, New Zealand, and the United Kingdom became the U.N. trustees of the island.

Nauru became self-governing in January 1966, and following a two-year constitutional convention, it became independent in 1968, led by founding president Hammer DeRoburt. In 1967, the people of Nauru purchased the assets of the British Phosphate Commissioners, and in June 1970, control passed to the locally-owned Nauru Phosphate Corporation. Income from the exploitation of phosphate gave Nauruans one of the highest living standards in the Pacific and per capita, in the world. In 1989, Nauru took legal actions against Australia in the International Court of Justice over Australia's actions during its administration of Nauru. In particular, Nauru made a legal complaint against Australia's failure to remedy the environmental damage caused by phosphate mining. Certain Phosphate Lands: Nauru v. Australia led to an out-of-court settlement to rehabilitate the mined-out areas of Nauru.