Papua New Guinea occupies the eastern half of the island of New Guinea plus the Bismarck Archipelago, Bougainville, and hundreds of smaller islands in the southwestern Pacific Ocean. The country contains 852 distinct languages, the highest linguistic diversity per capita on Earth. The 2021 census recorded a population of 9,119,010 people distributed across four regions: the Highlands, the Momase coast, the Southern region, and the New Guinea Islands. Port Moresby, the capital, had a population of 364,145 in 2011. More than 85 percent of Papua New Guineans live in rural areas, most practicing subsistence agriculture. The terrain divides communities into valleys separated by the Owen Stanley Range and Central Range, with Mount Wilhelm reaching 4,509 meters and Mount Giluwe 4,368 meters.
The archaeological record at Kuk in the Western Highlands documents continuous swamp cultivation from 10,000 years ago, making it one of the world's earliest independent centers of agriculture. Kuk became a UNESCO World Heritage Site in 2008 based on evidence of taro cultivation from approximately 8000 BCE and banana cultivation from around 5000 BCE. Human settlement in Papua New Guinea dates to at least 40,000 years before present based on archaeological sites in the Huon Peninsula. The Lapita people arrived in the Bismarck Archipelago approximately 3,500 years ago, bringing pottery and voyaging technology that later spread throughout the Pacific. These Austronesian speakers settled coastal areas and islands while earlier Papuan-speaking populations remained in the interior highlands.
European contact began when Portuguese navigator Jorge de Meneses sighted the northern coast in 1526. Spanish explorer Yñigo Ortiz de Retez named the island "Nueva Guinea" in 1545 because he thought the inhabitants resembled people from the Guinea coast of Africa. The Netherlands claimed the western half of New Guinea in 1828. Germany annexed the northeastern quarter of New Guinea in 1884, naming it Kaiser-Wilhelmsland, and also took control of the Bismarck Archipelago and the northern Solomon Islands. Britain declared a protectorate over the southeastern quarter in 1884, transferring administration to Australia in 1906 as the Territory of Papua. Australian forces captured German New Guinea in 1914 during World War One. The League of Nations granted Australia a mandate over the former German territory in 1920.
The Kokoda Track became a major battleground between July and November 1942 when Japanese forces attempted to capture Port Moresby by advancing overland from the northern coast. Australian and Papuan forces stopped the Japanese advance at Ioribaiwa Ridge, 48 kilometers from Port Moresby, in September 1942. Allied casualties on the Kokoda Track campaign totaled approximately 625 killed and 1,055 wounded. Rabaul on New Britain became Japan's major base in the South Pacific, holding an estimated 110,000 Japanese troops by war's end. Allied bombing destroyed much of Rabaul between 1943 and 1945. The Tavurvur and Vulcan volcanoes erupted in 1994, burying much of what remained of Rabaul under volcanic ash, leading to the relocation of the provincial capital to Kokopo.
Australia combined the Territory of Papua and the Territory of New Guinea into one administrative unit in 1949. The House of Assembly, Papua New Guinea's first elected legislature, convened in 1964 with 64 members. Internal self-government began in December 1973 under Chief Minister Michael Somare. Papua New Guinea became fully independent on September 16, 1975, remaining within the Commonwealth with Elizabeth II as head of state represented by a governor-general. The Constitution established a Westminster parliamentary system with a unicameral National Parliament. Bougainville declared independence as the Republic of the North Solomons on September 1, 1975, but rejoined Papua New Guinea sixteen days later after negotiations granted the province extensive autonomy.
A civil war erupted on Bougainville in 1988 when landowner grievances against the Panguna copper mine escalated into armed conflict. The Bougainville Revolutionary Army fought Papua New Guinea government forces until a ceasefire in 1998. The Bougainville Peace Agreement, signed on August 30, 2001, granted Bougainville autonomy and the right to hold an independence referendum. The Autonomous Bougainville Government formed in 2005. A non-binding referendum held from November 23 to December 7, 2019 resulted in 98.31 percent voting for independence from Papua New Guinea. Negotiations between the Papua New Guinea government and Bougainville continue regarding the timeline and terms of potential independence.