Colonial powers claimed land through conquest and treaties signed under pressure, then extracted resources, labor and taxes. They often ruled through racial hierarchies that placed Europeans at the top. The transatlantic slave trade, which forcibly moved millions of Africans to the Americas, was built to supply colonial plantations.
The US was founded as a set of British colonies and later became a colonial power itself. After the Spanish-American War of 1898, it took control of Puerto Rico, Guam and the Philippines. In the Insular Cases of 1901, the Supreme Court ruled that the Constitution did not fully apply in these territories, a doctrine still in force. In 1893, US-backed businessmen overthrew the Hawaiian Kingdom, and Congress formally apologized for that in 1993.
Colonialism's effects continue. About 3.5 million US citizens live in territories without voting representation in Congress or a vote for president. Colonial borders, debts and extraction still shape global inequality. Colonialism is closely related to settler colonialism, in which colonizers come to stay and replace the original people.