The Ganghwa Island incident or the Japanese Battle of Ganghwa (Korean: 운요호 사건 [雲揚號事件] Unyo-ho sageon meaning "Un'yō incident"; Japanese: 江華島事件 Kōka-tō jiken) was an armed clash between the Joseon dynasty of Korea and Japan which occurred in the vicinity of Ganghwa Island on September 20, 1875.
From 1910 to 1945, Korea was ruled by the Empire of Japan as a colony under the name Chōsen (朝鮮), the Japanese reading of "Joseon".
Japan first took Korea into its sphere of influence during the late 1800s. Both Korea (Joseon) and Japan had been under policies of isolationism, with Joseon being a tributary state of Qing China. However, in 1854, Japan was forcibly opened by the United States. It then rapidly modernized under the Meiji Restoration, while Joseon continued to resist foreign attempts to open it up. Japan eventually succeeded in forcefully opening Joseon with the unequal Japan–Korea Treaty of 1876.