From 1941 until his death, Mendelsohn lived in the United States and taught at the University of California, Berkeley. Until the end of World War II his activities were limited by his immigration status to lectures and publications. However, he also served as an advisor to the U.S. government. For instance, in 1943 he collaborated with the U.S. Army and Standard Oil in order to build "German Village", a set of replicas of typical German working-class housing estates, which would be of key importance in acquiring the know-how and experience necessary to carry out the firebombing of Berlin. In 1945, he established himself in San Francisco. From then until his death in 1953 he undertook various projects, mostly for Jewish communities.