In 1898, the United States acquired Puerto Rico, Guam, and the Philippines following its victory in the Spanish-American War. This sudden expansion presented an unprecedented constitutional dilemma: did the US Constitution automatically follow the flag into these newly acquired lands? In a series of Supreme Court decisions known as the Insular Cases starting in 1901, the court answered with a resounding 'not necessarily.'
Led by opinions from Justice Henry Billings Brown, the court created a brand-new distinction between 'incorporated' and 'unincorporated' territories. Incorporated territories, like Alaska and Hawaii at the time, were on a pathway to statehood and enjoyed full constitutional protections. Unincorporated territories, however, belonged to the United States but were not part of it.
Residents in these areas were granted only 'fundamental' constitutional rights, while 'procedural' rights like jury trials were withheld unless explicitly extended by Congress. This legal framework allowed the US government to collect tariffs on goods imported from Puerto Rico while denying its citizens full rights under the Constitution. Justice John Marshall Harlan famously dissented, arguing that the Constitution could not be turned on or off at the whim of Congress.
Despite being criticized as racist relics of an imperial era, the Insular Cases remain the foundational precedent governing the legal status of modern US territories including Puerto Rico, Guam, American Samoa, and the US Virgin Islands.