Livingstone advocated the establishment of trade and religious missions in central Africa, but abolition of the African slave trade, as carried out by the Portuguese of Tete and the Arab Swahili of Kilwa, became his primary goal. His motto—now inscribed on his statue at Victoria Falls—was "", a combination that he hoped would form an alternative to the slave trade, and impart dignity to the Africans in the eyes of Europeans. He believed that the key to achieving these goals was the navigation of the Zambezi River as a Christian commercial highway into the interior. He returned to Britain to garner support for his ideas, and to publish a book on his travels which brought him fame as one of the leading explorers of the age.