De Kiewiet emigrated to the United States in 1929 when he was offered a position teaching European history at the University of Iowa. In 1941, he joined the faculty of Cornell University, where he taught modern European history and pursued his research interests in British colonial policy, particularly in South Africa.
De Kiewiet's decision to emigrate to the United States in 1929 was prompted by an offer to teach European history at the University of Iowa. Two years later, in 1941, he joined the faculty at Cornell University, where he taught modern European history and explored his research interests in British colonial policy, with a specific emphasis on South Africa.