In 1937, Kook began his career as an international spokesperson for the Irgun and Revisionist Zionism. He first went to Poland, where he was involved in fundraising and establishing Irgun cells in Eastern Europe. It was there that he met the founder of the Revisionist movement, Ze'ev Jabotinsky, and became friends with his son Ari. At the founders' request, Kook traveled to the United States with Jabotinsky in 1940, at United States Holocaust Memorial Museum where he soon served as the head of the Irgun and revisionist mission in America, following the elder's death in August. This assignment was clandestine, and Kook publicly denied he was affiliated with the Irgun many times while in America.
