This research puts an emphasis on clarifying whether the education for international understanding(EIU) is still relevant to the changing global environment of the 21st century by the socio-historic approach of education to the changes of international communities before and after 1974 when EIU recommendation were adopted by UNESCO Assembly. EIU is the comprehensive peace education through international understanding and cooperation based on the principle of friendly relations between people and States having different social and political systems and on the respect for human rights and fundamental freedoms. Thus EIU aims to raise the glocal(global+local) citizenship with which an individual stands in the field of life and lives for the purpose of thinking globally, acting locally beyond supranational global citizenship education against a narrow-minded nationalism. Based on the socio-historical review of the transitional stages of EIU, the first period of reorganizing world system after the 2nd world war, 1945-1968 is characterized as UN-centered EIU. The 2nd cold-war between the East and the West period, 1968-1989 is focused on the disarmament-peace education. The 3rd generalization of neo-liberal globalization period, 1989-2008 is for the EIU based on universal values such as peace, human rights and democracy. The 4th contradiction of the neo-liberal globalization period, since 2008 is seen global citizenship centered EIU. As a consequence of socio-historic review, EIU is seen a relevant terminology towards the 21st century for the purpose of raising symbiotic human beings coping for the glocal agenda.