In the United States, Jaisohn conducted medical research at the University of Pennsylvania and later became a successful printer and stationer in Philadelphia. As he heard the news of the March First Movement (1919), a nationwide protest against ruthless Japanese rule in Korea, Jaisohn convened the First Korean Congress which was held in Philadelphia for three days. After the Congress, Jaisohn devoted his energies and private properties for the freedom of Korea. He organized the League of Friends of Korea in 26 cities with the help of Rev. Floyd Tomkins, and established the Korean Information Bureau and published a political journal Korea Review to inform the American public of Korean situations and to persuade the US government to support the freedom for Koreans.