For centuries, Korea had been a client state of China, providing tribute and much coal and iron. With Japan's growing modern technology, much of it dependent on exactly that, it saw Korea as a prime target for its growing military power. Requests and demands that China open Korea to Japanese trade were rebuffed, and so, Japan used this as an excuse to go to war with China. The ensuing conflict, the First Sino-Japanese War, was fought for about nine months between 1894 to 1895, and it resulted in another Chinese defeat. This gave Japan control of Korea, which it absorbed and colonized, and Japan also forced China to cede Taiwan to them. Japan also demanded the same rights within Chinese coastal cities as the Europeans and Americans had.

In 1876, Korea and Japan had signed a treaty, opening up trade between the two countries. Huang Zunxian, the Chinese ambassador to Korea, recommended that Korea maintain friendly relations with Japan. He felt that Japan would counterbalance any undesirable influence by Russia. At that time, Japan wasn't seen as a threat to the power of China. Japan was also interested in a cordial relationship with the US to further balance any possible threat from Russia. However, when the Americans established relations with Korea, they overlooked the fact that Korea had a history of being a tributary state of China, which started back in 1637. The US felt that Korea should be considered an independent state. The skilled statesman Li Hongzhang was in charge of the Chinese-Korean policy and presented a compromise that would satisfy both the US and China. So, the Japan-Korea Treaty was amended to state that Korea was "an independent state enjoying the same sovereign rights as does Japan."

Li Hongzhang spoke with Korean representatives and recommended that they emulate the Self-strengthening Policy that China had started and introduce reforms that would help them relate to other countries from a position of strength-not overwhelming strength but at least equal strength. The Chinese then sent over a military unit to train Korean soldiers in warfare techniques and provided them with upgraded weapons.

The Japanese were ambivalent about Korea's interest in reform. Some were very much in favour of it and wanted to participate in helping Korea develop, but other Japanese preferred that Koreans focus on these improvements by themselves and thus be more passive on the world stage. Regardless of the differences of opinion in Japan, the Korean Prince Regent Heungseon Daewongun saw to it that reform efforts were started.

Korea's relationships with China and Japan were tested in 1882 when a riot broke out in Korea during a drought. It started in Imo but inexplicably spread to the Japanese legation in Korea. Six Japanese were killed, and riots broke out throughout the city.

Japan then deployed four warships to Korea, and China sent in 4,500 troops. The two countries were now competing for control over Korean affairs. As a result of the Imo Incident, Korea made reparations and penalized the chief perpetrators of the rebellion, which had resulted in the deaths of Japanese representatives. When the Koreans blamed Heungseon Daewongun for the riot, the Chinese interfered by taking him to China, where he was confined. China wanted the Korean reforms to move along gradually, while Japan wanted them to make rapid improvements.

The Japanese dispatched a fleet into the Korean harbors of Pusan and Chempulpo, but they assured Li Hongzhang that they had no intention of attacking. They indicated that they simply wanted to balance off the Chinese forces already in the country. King GoJong of Korea insisted that the Japanese depart. However, Japan adamantly refused.

In 1894, tensions between Japan and China reached a pivotal moment in terms of their relations with Korea. The First Sino-Japanese War was very short, lasting a little over eight months. Despite the fact that they had revitalized their military, China wasn't ready. In July, the Japanese vessels Naniwa, Akitsushima, and Yoshino captured and sunk the Kowshing, a British transport ship subcontracted by China to carry members of the Green Standard Army and Eight Banners Army into Asan, Korea.

The Japanese heavily outnumbered the Chinese, and at the Battle of Seonghwan, they defeated the Chinese, placing them within fifty miles of Seoul. The bulk of the Chinese shored up their defences in northern Korea, sensing that the Japanese would make a strike there. More Chinese were stationed in northern Korea than at the prior battle near Asan. Most were guarding the capital city of Pyongyang. The Japanese separated their forces into three divisions. Two engaged the Chinese at opposing diagonal corners of the city walls, and the third division attacked from the rear. After the Japanese won this battle, the Chinese pulled out of the north and withdrew toward the mouth of the Yalu River, which feeds out of the Yellow Sea, near the Chinese/Korean border.

At the Battle of the Yalu River, which took place in 1894, the Japanese navy's frontal formations proved to be superior to those of the Chinese. At the end of this one-day battle, China's Beiyang fleet withdrew. Chinese troops then moved to defend their own homeland in Manchuria when they saw the Japanese were moving toward their shores. However, the Japanese were able to capture the Chinese outpost of Hushan before moving on land to capture six towns in Manchuria.

In Port Arthur, the Japanese reported that they saw the decapitated head of a dead Japanese soldier on display. They retaliated with an indiscriminate massacre of thousands of Chinese soldiers and civilians. The estimates of the number killed i the Port Arthur Massacre differ vastly.

In the city of Weihaiwei in northeast China, Chinese soldiers stayed behind the fortification walls when the Japanese placed the city under siege. The Chinese abandoned the fort in the bitter cold of January 1895, and the battle moved to the Yellow Sea. After winning the Battle of Weihaiwei, the Japanese took over the Liaodong Peninsula, which borders northwestern Korea.

The ground forces of both parties were engaged in Manchuria and its environs, and the Japanese conquered six cities there. They then headed toward the Manchurian capital, Mukden. The Japanese captured the town of Haicheng on the Liaodong Peninsula. The Chinese made four attempts to retake the city but failed every time. As they were anxious to end the war, the Japanese decided they wanted to take either Mukden or Beijing, as losing either one would greatly cripple the Chinese forces.

The Japanese then surprised China and the international observers by capturing the Pescadores Islands in the Taiwan Strait. The Japanese wanted control of the Pescadores because that would be their key to gaining control of Taiwan. Those islands could have been used by Japan to prevent the arrival of Chinese reinforcements to Taiwan, as well as open the gates to gain Taiwan in a subsequent Treaty of Shimonoseki.

The war demonstrated the failure of the Qing dynasty's attempts to modernize its military and fend off threats to its sovereignty, especially when compared with Japan's successful Restoration of the Meiji and led to the Self-Strengthening Policy. For the first time, regional dominance in East Asia shifted from China to Japan; the prestige of the Qing dynasty, along with the classical tradition in China, suffered a major blow. The humiliating loss of Korea as a tributary state sparked an unprecedented public outcry. Within China, the defeat was a catalyst for a series of political upheavals led by Sun Yat-sen and Kang Youwei, culminating in the 1911 Xinhai Revolution.