This study is to review on the restriction factors against then Korean Peninsula unification. The restriction factors are the Korean War and the Armistice, NK's provocations against the ROK, NK's strong military power and Nuclear weapon development, and NK's unification policy. The Korean War was the International War that executed the massive of weapon, and the Limited War. Major weapon system employed in the war, were the conventional weapons though the nuclear, chemical and biological weapon had developed already, theory of responsibility of breakout of the Korean War. After the Korean War, North Korea developed secretly the nuclear weapon, and executed the nuclear test experiments three times on 9 October 2006, 25 May 2008, and 12 February 2013. Because of the North Korea will use the strategy of unification propaganda against the ROK based on the superiority of military power, the security dilemma in the Korean Peninsula will be escalated. The ROK-US Alliance has contributed to the national stability and economic development along with the national security side, the ROK-US Alliance has been becoming a key axis role during over sixty years, and the role will continue in the future.