a different civilization, and began to doubt their own superiority. The mainline Protestant denomination missionary work declined rapidly.David A. Hollinger, Protestants abroad: how missionaries tried to change the world but changed America (2017) pp 59-93. In their place Chinese Christians increasingly took control. Furthermore, there was a rapid growth of fundamentalist, Pentecostal and Jehovah Witness missionaries who remained committed to the conversion process. The May Fourth Movement criticized all traditional beliefs and religions. The 1922 study The Christian Occupation of China presented view of the liberal wing of the missionary establishment that control should be turned over to Chinese, but the unfortunate title made matters worse. The Anti-Christian campaigns of the early 1920s, and the Northern Expedition of 1925–27 led to the unification of China under the Nationalist Party. Liberal missionaries welcomed the opportunity to participate in the development of the Chinese nation, but the mission enterprise was attacked. As anti-imperialism grew, Christian schools were subjected to government regulation which required that all organizations have Chinese leadership. Many missionaries left China and support in home countries waned, partly because of economic problems during the Great Depression. Criticism and calls for reform came from within the missionary community. Partly as a result of the Fundamentalist–Modernist Controversy missions came under questioning. Novelist and missionary Pearl S. Buck for example, returned to the United States in 1932 to ask "Is There a Case for Foreign Missionaries?." Buck's twin biographies of her parents, Fighting Angel and The Exile, dramatized the charges that foreign missions were a form of imperialism. Another skeptical note was sounded by the massive study commissioned by John D. Rockefeller, Jr. entitled "Rethinking Missions" which cast doubt on a wide range of missionary activities. In 1934 John and Betty Stam were murdered by Communist soldiers. Their biography The Triumph of John and Betty Stam (Chicago: Moody Press, 1982) was written by Mrs. Howard Taylor, a fellow missionary with the China Inland Mission. It inspired a new generation of missionaries to seek to work in China despite civil war and the anti-missionary views of many Chinese. When the Japanese invaded China in World War II in 1937, the China Inland Mission and many other missionary organizations moved their headquarters up the Yangzi River to Chongqing. After Japan went to war with the Western countries in 1941, the Japanese interned Western civilians, including about 1,000 Protestant missionaries, in camps until the end the