This thesis explores briefly two experimental cases, Czechoslovakia and Poland, where between 1919 and 1938, efforts were made to solve the “minority problem." This thesis consists of five basic parts: Chapter I, an introduction that defines or describes such concepts as nationalism, nation, state, and minority; Chapter II that succinctly presents backgrounds and problems of minorities in Czechoslovakia (Germans, Magyars, Ruthenians, and Jews), and Poland (Germans, Jews and Ukrainians); Chapter III that analyzes the provisions of the Minority Treaties prepared by the principal Allied Powers at the end of World War I to protect minority rights within Czechoslovakia and Poland; Chapter IV that examines the implementation and results of the planned protection of minority rights in Czechoslovakia and Poland between 1919 and 1938; and Appendices that illuminate the minority problem in the two states.