The First Sino–Japanese War ( 中日甲午战争 ) was a war fought between Japan and Qing Dynasty, which was officially declared on August 1, 1894, though some naval fighting had already taken place. The invasive Japanese army defeated the Chinese in a series of battles around Seoul and Pyeongyang, forcing them north, and by November 21 the Japanese had taken the fishing village of Lushun ( 旅顺 ) at the tip of the Liaodong Peninsula ( 辽东半岛 ) . Following the Chinese capitulation at Port Arthur it exited that the Japanese army massacred thousands of the city's Chinese inhabitants in cold blood, an event that came to be called the Port Arthur massacre.

The Japanese navy devastated Qing's Beiyang fleet ( 北洋舰队 ) off the mouth of the Yalu River at the Battle of Yalu on September 17, 1894. The Chinese fleet having lost 8 out of 12 warships, retreated behind the fortifications of the Weihai ( 威海 ) naval base, and was soon afterwards caught by surprise when the Japanese landed troops they had staged at Port Arthur on the opposite Liaodong Peninsula outflanking the harbor defenses. The unexpected attack shattered the ships in harbour with shelling from the landward side. After Weihaiwei ( 威海卫 ) 's fall on February 2 and an easing of harsh winter conditions, Japanese troops pressed into Manchuria.

Faced with these repeated defeats Qing signed the Treaty of Xiaguan ( 下关条约 ) in April, 1895, agreeing by treaty to stay out of Korea and ceding a large portion of eastern Manchuria, including the Liaodong portion of the modern Liaoning province. Additionally, the island of Taiwan was also ceded to the Japanese. It also drastically accelerated the Imperialist demands laid on the dynasty by western powers, in particular Britain, France, Germany, and Russia. For example, the latter, after the diplomatic slap in the face given to Japan in the Triple Intervention, moved almost immediately to occupy the entire Liaodong Peninsula and, especially to fortify Port Arthur despite vigorous protests from China, Japan, as well as the United States — all three favoring an Open Door Policy in Manchuria ( 满洲 ) .

The degree to which Western powers were emboldened can be inferred by examining the actions of the powers in the Boxer Rebellion, where they all but fell over in the rush to blame the Qing government for the rebellion of the resentful Chinese population. The result was further humiliating concessions from the by-then moribund Chinese Empire.