During World War II, he supported giving aid and asylum to refugees. This was in opposition to Luis López de Mesa, the Minister of Foreign Affairs, who prohibited the entry of Jews into Colombia. Due to this resurgence of Conservative ideology in the 1940s, Arciniegas felt that he and his family were in danger and moved to the United States, taking advantage of an offer to teach at Columbia University. He lived in New York for ten years (1947–57). At this time, he wrote his most important and most often banned book, "Entre la Libertad y el Miedo" (Between Freedom and Fear, 1952). The work analyzes a critical period in Latin-America, when seven dictators were in power at the same time. He also criticized the U.S. State Department for its conciliatory behavior towards these regimes and, as a result, was detained for questioning several times after returning from trips abroad.