Albizu Campos was honorably discharged from the Army in 1919, with the rank of First Lieutenant. However, his exposure to racism during his time in the U.S. military altered his perspective on U.S.- Puerto Rico relations, and he became the leading advocate for Puerto Rican independence.
In 1919, Albizu returned to his studies at Harvard University, where he was elected president of the Harvard Cosmopolitan Club. He met with foreign students and world leaders, such as Subhas Chandra Bose, the Indian Nationalist leader, and the Hindu poet Rabindranath Tagore. He became interested in the cause of Indian independence and also helped to establish several centers in Boston for Irish independence. Through this work, Albizu Campos met the Irish leader Éamon de Valera and later became a consultant in the drafting of the constitution of the Irish Free State. Also while at Harvard University he co-founded the university's Knights of Columbus chapter along with other Catholic students.
In 1919, José Coll y Cuchí, a member of the Union Party of Puerto Rico, took followers with him to form the Nationalist Association of Puerto Rico in San Juan, to work for independence. They gained legislative approval to repatriate the remains of Ramón Emeterio Betances, the Puerto Rican patriot, from Paris, France.