His research has centered on the intersections of race, labor, migration, and borders in the Americas, and the history of the United States in the Asia-Pacific world. His first book Pacific Connections: The Making of the U.S.-Canadian Borderlands (2012) was the winner of the 2014 Association for Asian American Studies History Book Prize and runner-up finalist for the 2013 John Hope Franklin Book Prize. He is currently working on book on the U.S. Occupation of Korea, focusing on the different ways Americans and Koreans imagined independence and how they struggled over its meaning. His research and writing has been supported by fellowships from the American Council of Learned Societies, the Andrew W. Mellon Foundation, Charles Warren Center at Harvard University, and the American Academy of Arts and Science.