Unlawfulness of Japan’s Colonization of Korean Peninsula: Korea’s Declaration of January 21, 1904, and Japan’s Violation of International Law

This article examines the illegality of Japan’s colonization of the Korean Peninsula, focusing on the period from the 1904 declaration of neutrality by the Korean Empire through the 1910 annexation. It argues that Japan’s military invasion and occupation of Korea constituted a serious violation of customary wartime international law, particularly the law of neutrality, as Korea’s neutrality was internationally recognized but disregarded by Japan. The paper analyzes the An Chunggun case, highlighting how Japanese courts ignored wartime international law and instead applied domestic criminal law, undermining Korea’s sovereignty. The study demonstrates that key treaties, such as the 1904 Protocol and the 1905 Protectorate Treaty (Eulsa Treaty), were invalid due to coercion, lack of ratification, and procedural defects. It further contends that the 1910 Annexation Treaty was also null and void, as it was based on these illegitimate agreements and lacked proper authorization. The article draws on historical and legal sources to show that Japan’s occupation was unlawful under both contemporary and modern international law. This conclusion aligns with the 2018 ruling of the Republic of Korea’s Supreme Court. The paper underscores the importance of recognizing these violations for historical justice and future reconciliation in East Asia.