Oceania is a geographic region that includes Australasia, Melanesia, Micronesia, and Polynesia. Spanning the Eastern and Western Hemispheres, it is often grouped as a continent, with Australia being the largest landmass. Within this region lies Nauru, the world's smallest island nation and the smallest independent republic. Covering only 21 square kilometers, Nauru has no official capital city, though the district of Yaren is the seat of government. Oceania is characterized by thousands of islands scattered across the Pacific Ocean, ranging from the volcanic peaks of Hawaii to the coral atolls of Kiribati. The region faces significant environmental threats due to climate change, particularly rising sea levels which threaten the existence of low-lying island nations. Culturally, Oceania is incredibly diverse, with indigenous populations having inhabited the islands for thousands of years before European exploration.