Albert Einstein was widely known during his lifetime for the development of the theory of relativity and work with physics in general. However, Einstein's political views were of public interest through the middle of the 20th century due to his fame and involvement in political, humanitarian and academic projects around the world. Einstein was a peace activist, a firm advocate of world federalism and world law. He was in favor of socialism, especially in his later life, detailing his economic views in a 1949 essay titled "Why Socialism?". Einstein's visible position in society allowed him to speak and write frankly, even provocatively, at a time when many people were silenced due to the rise of the Nazi movement. Once living in the United States, Einstein often objected to the mistreatment of African Americans and worked with various civil rights organizations. Einstein was a prominent supporter of both Labor Zionism and Jewish-Arab cooperation.