What Were They Dying For? The Battle of Okinawa in 1945 was called "among the most intense and famous in military history" by Churchill. During this battle, the Japanese Special Attack Unit—Kamikaze—initiated suicide attack which was designed to destroy battleships. Those young pilots under 24 attempted to crash their aircraft into enemy ships. Around 19% Kamikaze aircraft succeeded in hitting their targets(Higgins, 2016). Warfare is an eternal and heavy topic in human history. However, this suicide terrorism that pilots intended to kill others by killing themselves is inhuman and eerie. What motivate themselves to suicide, and what they were dying for? In the record left by kamikaze participants, three contents are mentioned most repeatedly: honor, family, and country (Orbell and Morikawa, 2011, 13). Therefore, Japanese Bushido culture, altruism, and nationalism should be taken into account when explaining motivation of the kamikaze suicide terrorism. The influence of Bushido culture on kamikaze could not be neglected. According to a research conducted by Liddle, religious belief is a leading factor in the occurrence of suicide terrorism. Although the majority of kamikaze participants are not Christians (Orbell and Morikawa, 2011, 13), the impact of unique Japanese Bushido culture is similar and strong also. Seppuku is a typical example in the Bushido culture. Warriors who lost honor would demonstrate his allegiance and courage by cutting the belly. As Arthur Knapp wrote in his book Feudal and Modern Japan, samurai is a thousand years of training in the law of honor, duty, and self-sacrifice. In poems and letters left by Kamikaze participants, 79% mentioned honorable and beautiful death (Orbell and Morikawa, 2011, 13), which is consistent with appreciation of the heroic spirit in Japanese culture. When sacrificing personal interests could reduce the threat from aggressors, honorable death would be in line with the loyalty and self-sacrifices in Bushido. Additionally, altruism is another important factor. Suicide terrorism happened probably because it provides benefits to relatives of terrorists (Liddle, Bush, Shackelford, 2011, 16). This kin altruism could be explained by Hamilton's kin selection theory. According to kin selection, if sacrificing oneself could increase the benefits of kin, then this sacrifice would be made. In Orbell and Morikawa’s research, over 52% mentioned "family love" or "I’m doing it for my family". Accordingly, their death in the war could bring both honor and benefits to their family and children. Their efforts and sacrifices against aggressors could increase the probability to win the battle, which also would increase the opportunity for their relatives to survive. Except for larger surviving chances, their family could obtain compensation from the government. Subsidies for martyrs in Japan are up to 800,000 dollars (2017). Therefore, even if they died and cannot pass their genes directly, their genetic kin would have a large number of opportunities to pass genes and benefit from their suicide behavior. Moreover, 70% of kamikaze participants mentioned that they died for the country and emperor (Orbell and Morikawa, 2011, 13). The kamikaze thought themselves died not just for their relatives but 100 million people in the country(Orbell and Morikawa, 2011, 19). According to kin selection, people are more willing to sacrifice themselves for people who have kin relationships with them (Buss, 2015, 225-248). Dying for other people in the country could not benefit their kin. So why do they have this kind of patriotism and nationalism that being willing to sacrifice themselves for the country? Considered a conflict between two alliances which consist of both kin and nonkin. The coalition whose members are only willing to sacrifice for kin would be less efficient compared with a kin-emotion based coalition. Therefore, the alliance based on kin emotion is more likely to win, and more likely to pass genes down. Consequently, genes that just having kin emotion with true kin members in the coalition would not be be favored by natural selection. On the contrast, genes that respond to all members in the coalition as if they were kin would be favored and passed down. In the kamikaze case, when the country is threatened by the Unites States and individual death could decrease the threat, members in the coalition would emerge kin emotion with others and then accept death. The willingness to sacrifice for relatives is transferred and expanded to sacrifice for people in the country. The letters and poems left by Japanese Kamikaze contained abundant themes related to honorable death, family love, and emperor. Those evidence suggest that motivation for this suicide terrorism is not only affected by the Bushido culture but also due to altruism and nationalism caused from kin selection. Although the three factors mentioned above are not the only reasons for kamikaze behaviors in the battle of Okinawa, they provide a possible way to understand suicide terrorism mechanism from evolutionary psychology perspective, and also a feasible process to understand the bright and dark side coexisting in human nature.