On June 4, the Korean king, Gojong, requested aid from the Qing government in suppressing the Donghak Rebellion. Although the rebellion was not as serious as it initially seemed and hence Qing reinforcements were not necessary, the Qing government still sent the General Yuan Shikai as its plenipotentiary to lead 2,800 troops to Korea.
According to the Japanese, the Qing government had violated the Convention of Tientsin by not informing the Japanese government of its decision to send troops, but the Qing claimed that Japan had approved this. The Japanese countered by sending an 8,000-troop expeditionary force (the Oshima Composite Brigade) to Korea. The first 400 troops arrived on June 9 en route to Seoul, and 3,000 landed at Incheon on June 12.
Additional Japanese troops arrive in Korea. Japanese prime minister Itō Hirobumi tells Matsukata Masayoshi that since the Qing Empire appear to be making military preparations, there is probably "no policy but to go to war". Mutsu tells Ōtori to press the Korean government on the Japanese demands.
In early June 1894, the 8,000 Japanese troops captured the Korean king Gojong, occupied the Gyeongbokgung in Seoul and, by June 25, replaced the existing Korean government with members of the pro-Japanese faction.
Japanese troops occupy Seoul, capture Gojong, and establish a new, pro-Japanese government, which terminates all Sino-Korean treaties and grants the Imperial Japanese Army the right to expel the Qing Empire's Beiyang Army from Korea.
On 25 July 1894, the cruisers Yoshino, Naniwa and Akitsushima of the Japanese flying squadron, which had been patrolling off Asan Bay, encountered the Chinese cruiser Tsi-yuan and gunboat Kwang-yi. These vessels had steamed out of Asan to meet the transport Kow-shing, escorted by the Chinese gunboat Tsao-kiang. After an hour-long engagement, the Tsi-yuan escaped while the Kwang-yi grounded on rocks, where its powder-magazine exploded.