- Puerto Rico: In July 1898, the American forces landed in Puerto Rico, during the Spanish-American War. The war ended in December that same year with the signing of the Treaty of Paris, which resulted in the United States acquiring Puerto Rico.
- Philippines: As a result of the war with Spain, the US also acquired the Philippines despite opposition from the local population. The US suppressed an extensive guerrilla campaign that lasted until the early 1902, and remained in the Philippines until 1946, when it finally achieved its independence.
- Hawaii: In 1898, Congress passed a joint resolution that annexed the Republic of Hawaii. Hawaii became the 50th US state in 1959.
- Cuba: Although Cuba wasn't formally annexed by the US, the US did exercise great influence over the country. The US imposed the Platt Amendment, which limited Cuban sovereignty, and Cuba was occupied by US forces on and off until the 1930s.
- Panama: In 1903, the US played a key role in Panama's separation from Columbia, in a move to build the Panama Canal. The canal zone remained under US control until the year 2000.