On July 23, 1894, their troops entered Seoul and seized Korean King Gojong, establishing a pro-Japan government. Two days later the first sea battle began, and soon the engagements spread to land forces, with 500 Chinese killed in their first skirmish. War was officially declared on August 1.
On September 17, Japanese warships destroyed eight of the 10 vessels in China's Beiyang Fleet, in the Battle of the Yalu River. The isolated Dingyuan was later scuttled.
In the Treaty of Shimonoseki that ended the war, China ceded Taiwan and the Penghu Islands to Japan "in perpetuity". Tokyo was to rule Taiwan until the end of World War II, and Chinese influence over Korea ended.
Now the tide has turned, and a visit by Xi to Seoul this month underlined how warm the China-Korea relationship is becoming, as their present leaders appear to share a mutual distaste for North Korea and a dislike of Japan.
Six months ago, to Japanese protests, China opened a memorial hall in Harbin railway station in tribute to a Korean, Ahn Jung-geun, who assassinated there the Japanese governor-general of Korea in 1909.
A four-part TV documentary series on the war, co-produced by the Central New Film Group and the PLA National Defence University, is now being screened.
About 20,000 troops are participating in Huoli 2014, a land-based exercise, and the Civil Aviation Administration has warned of "widespread delays" for flights to and from Shanghai and other cities from Qingdao down to Nanjing, due to air combat exercises.
Beihang University professor and naval expert Liu Janping says these exercises are more combat-oriented, last longer, and require closer cross-unit co-operation, at the express request of Xi, who is also chairman of the Central Military Commission.
A China Central TV report noted this war marked China's first military defeat to Japan.
It quoted Li Zhanteng, who works as a researcher at a centre devoted to the defeat, as saying that "history provides solid proof that the war was the root of Japan's militaristic strategy of invading China and other parts of Asia" - a strategy which, Chinese officials have been hinting recently, has been revived under Prime Minister Shinzo Abe.
The report said it was not the Chinese forces but "the corruption and fatuity" of the Qing dynasty that were to blame for the defeat: "This conclusion has obvious modern-day applications, because China's leadership is now emphasising both reform and a new focus on the country's military build-up."
