危機
↑ Wisner B., P. Blaikie, T. Cannon, and I. Davis. "At Risk – Natural hazards, people's vulnerability and disasters". Wiltshire: Routledge. 2004. ISBN 0-415-25216-4.
↑ Numbers of threatened species by major groups of organisms (1996–2016). IUCN. 2016.なお、IUCNは絶滅寸前(CR)、絶滅危惧種(EN)、および危急種(VU)の3カテゴリーに入る種を「絶滅が危惧される種」としている。
↑ Endangered languages. UNESCO. Accessed August 10, 2012.
↑ Lebow, RN. "Between Peace and War: The Nature of International Crisis". pp.7-10. The Rancho Bernardo Hopkins University Press, 1981. ISBN 0-8018-2311-0.
↑ Shlaim, Avi. "The United States and the Berlin Blockade, 1948–1949: a study in crisis decision-making". p.5. Berkeley, California: University of California Press. 1983.