In the case of Gonzales v. Williams in 1903, Isabel Gonzalez, a woman from Puerto Rico, was denied entry into New York under the Immigration Act of 1891 which classified her as an "alien immigrant". She challenged this decision arguing that she should be considered a U.S citizen since Puerto Rico had been annexed by the United States following the Spanish-American War. The Supreme Court ruled in favor of Gonzalez but did not declare her to be a U.S citizen. Instead, they decided that while individuals from territories owned by the United States were not foreign and could enter mainland America freely without immigration restrictions, they were also not automatically granted citizenship status. This ruling led to further discussions about citizenship rights for people living in American territories and eventually contributed to legislation granting them statutory citizenship.

In the dissenting opinion for Gonzales v. Williams, Justice Harlan disagreed with the majority's decision to avoid answering whether or not a Puerto Rican was an alien under immigration laws. He argued that this question should have been addressed directly and answered in the negative, as he believed that citizens of Puerto Rico were not foreign to the United States but rather part of it due to its status as a U.S territory. Therefore, they should be considered U.S citizens and not subject to immigration laws designed for foreigners entering America from other countries. His view was based on his interpretation of both constitutional law and international law principles regarding territorial acquisition.