This is the online Appendix to the article published in Historical Social Research 44 (4): 269-92. doi: 10.12759/hsr.44.2019.4.269-292. The Korean War, having started on June 25, 1950, has never formally ended. As the two Koreas are technically still at war, the conflict on the Korean Peninsula has become intractable. The goal of this study is to explore the attitudes of South Koreans living in the intractable conflict about how to achieve peace. To fulfill this goal, we conducted a nation-wide survey to investigate attitudes toward militant and cooperative internationalism. We also measured various variables involved with the intractable conflict. Our results indicate that the value of international harmony and equality as well as attitudes toward peace are the best predictors of cooperative internationalism, while the value of international harmony and equality as well as the attitudes toward war were the strongest predictors of militant internationalism. Our results also suggest that the tendency to regard inter-Korean relations as zero-sum relations and the attitudes toward peace mediated the relationship between international harmony and cooperative internationalism, while the zero-sum perception and attitudes toward war on the Korean Peninsula mediated the same value factor and the cooperative internationalism. Possible implications are discussed.