Germany, Australia, Japan, the U.S., and Papua New Guinea colonized and settled Bougainville Island because of its resources and placement in the Southwest Pacific. The island is named after Louis de Bougainville, a Frenchman who documented the island in 1765. Before WWI, Germany claimed the island and missionaries spread Christianity. Australia removed Germany during WWI and moved islanders into larger settlements to simplify supervision and assimilation. Later during WWII, Japanese forces took the island. The U.S. Military quickly removed Japan from Bougainville Island in 1944 because it was a strategic outpost for U.S. forces to safely go after bombing Japan. Until then there was nowhere U.S. forces could land before running out of fuel.

After WWII, Australia again took control over Bougainville Island. In the 1960s, copper and gold was found on the island, sparking conflict between Bougainville residents and mining companies. Bougainville Island gained independence from Australia as part of Papua New Guinea in 1975, but was then denied its own independence. In 1988, civil war began between Bougainville Island and Papuan New Guinea when the Bougainville Revolutionary Army started forcing mines to close. Peace talks began in 1997, but did not fully resolve the tensions. 

Between November 23rd and December 7th of 2019, the island hosted the 2019 Bougainvillean Independence Referendum. The referendum questioned whether there should be greater autonomy within Papua New Guinea or full independence. The results were overwhelmingly for independence (98.31%). In 2021 leaders from Papua New Guinea and Bougainville Island agreed that Bougainville will gain full independence from Papua New Guinea by 2027 and become the world's newest nation.