The Pacific Islands region consists of thousands of tropical islands scattered across the vast Pacific Ocean. While some islands are high volcanic islands with fringing and barrier reefs, others are low-lying coral atolls that formed on sunken volcanic peaks. Major powers colonized many islands over centuries, though France retains the largest Pacific colonial empire today. The islands are divided into three culturally distinct regions - Melanesia, Micronesia, and Polynesia - comprising many independent nations and territories across a massive expanse of ocean.