For over 15 centuries, the relationship between Japan and Korea was characterized by cultural exchanges, economic trade, political contact and military confrontations, all of which underlie their relations even today. During the ancient era, exchanges of cultures and ideas between Japan and mainland Asia were common through migration via the Korean Peninsula and/or diplomatic contact and trade between the two. Buddhism, Chinese-influenced cuisine, Han characters and other technology came to Japan via Korea and the East Sea.^[1]

Since 1945, relations involve three states: North Korea, South Korea and Japan. Japan cut off Korea from Qing Chinese suzerainty and for Japan, a high priority in the late 19th century, fighting wars with those two countries on the issue. Japan took control of Korea with the Japan-Korea Annexation Treaty of 1910. When Japan was defeated in World War II, Soviet forces took control of the North, and American forces took control of the South, with the 38th parallel as the agreed-upon dividing line. South Korea became independent as of August 15, 1945, and North Korea as of September 9, 1945. In June 1950, North Korea invaded and almost conquered South Korea, but was driven back by the United Nations command, leading South Korean, American, European and international forces. North Korea was nearly captured, with the United Nations intending to roll back Communism there.^[2] However, China entered the war, pushed the UN forces out of North Korea, and a military stalemate resulted along the lines similar to the 38th parallel. An armistice was agreed on in 1953, which is still in effect, and the cease-fire line of that year remains the boundary between North and South.^[3]

Diplomatic relations between Japan and South Korea were established in 1965. In the early 2000s, the Japanese–South Korean relationship soured when the Japanese Prime Minister Junichiro Koizumi visited the Yasukuni Shrine every year during his term. Furthermore, conflicts continue to exist over claims of the Liancourt Rocks (known in Korea as "Dokdo") – a group of small islets near Korean island "Ulleungdo".

Bilaterally and through the Six-Party Talks, North Korea and Japan continue to discuss the case of Japanese citizens abducted by the North Korean government during the 1970s and 1980s, although there are no existent diplomatic relations between the two; Japan does not recognize North Korea as a sovereign state.

In recent decades, irreconcilable disputes over history and history textbooks have soured relations between Japan and the two Koreas. The debate has exacerbated nationalist pride and animosity, as teachers and professors become soldiers in an intellectual war over events more than a half-century old or even two millennia older. Efforts to reach compromise agreements have failed. Meanwhile, a much less controversial, less politicized and more study-oriented historiography has flourished in Western nations.^[4][5] In 2013, polls reported that 94% of Koreans believe Japan "Feels no regret for its past wrongdoings," while 63% of Japanese state that Korean demands for Japanese apologies are, "Incomprehensible."^[6]

Relations between Korea and Japan go back at least two millennia. After the 3rd century BC, people from the Three Kingdoms (Goguryeo, Baekje and Silla) and Gaya in the Korean Peninsula, started to move southwards into the Kyushu region of Japan.^[7] Knowledge of mainland Asia was transmitted via Korea to Japan. According to the description of the Book of Wei, Yamatai-Koku kingdom in Japan and Four Commanderies of Han had diplomatic exchanges around the 3rd century. There are indications of cross-border political influence, but with varying accounts as to in which direction the political influence flowed. Buddhism was introduced to Japan from this Korean monarchy.^{[8][9][10][11][12][13][14][14][15]} By the time of the Three Kingdoms period of Korea, Baekje and Silla sent their princes to the Yamato court in exchange for military support to continue their already-begun military campaigns around 400.^[16][17]

Uija, the last king of Baekje (reigned 641–660), formed an alliance with Japan and made Prince Buyeo Pung and King Zenko stay there as their guests. In 660, Baekje fell when it was attacked by Silla, who was in alliance with Tang China. Former generals of Baekje, including Gwisil Boksin, asked Japan to return Prince Buyeo Pung and requested military aid. In 663, Japan, supporting Baekje, was defeated by the allied forces of Silla and Tang China in the Korean Peninsula (the Battle of Baekgang), and the restoration of Baekje ended up in failure. After the fall of Baekje, Japan took in many Baekje Korean refugees who were mainly craftspeople, architects and scholars who played a major role in the social development of Japan during that period. While at the same time hostility between Japan and Silla escalated. Empress Jitō honored King Zenko by giving him the hereditary title of Kudara no Konikishi and allowed him to pass on his royal lineage to future generations. According to the Shoku Nihongi (続日本紀), Takano no Niigasa came from a background of the naturalized clansmen Yamato-no-Fuhito (和史) and was a 10th-generation descendant of King Muryeong of Baekje. She was chosen as a wife for Emperor Kōnin and subsequently became the mother of Emperor Kanmu.^[18][19]

Japan has had official contact with the Chinese since the 7th to 8th centuries. Chinese culture was introduced to Japan via the Korean Peninsula, but the Korean value slumped when Chinese culture was introduced directly via Japanese missions to Tang China. Emperor Kanmu severed diplomatic relations with Silla in 799.^[20] From the early 9th–11th centuries, Japanese pirates plundered the southern region of Korean Peninsula and Korea-Japan relations deteriorated.^[21][22]

During the middle Kamakura period, Japan suffered from the invasions of the Mongol Empire (Yuan dynasty), which was then dominant on the continent, and its partner kingdom, the Goryeo of Korea. The History of Yuan states that the Mongol invasions of Japan began with King Chungnyeol of Goryeo "persistently recommending an expedition to the east to Yuan's emperor in order to force Japan to become its vassal state."^[23] In order to invade Japan, the Mongols ordered the Korean king to manufacture 1,000 warships.^[24] The two Mongol – Korean fleets were destroyed by storms, giving rise to the myth of the Kamikaze, the divine winds that protected Japan. At the time of Mongol invasions of Japan, Japanese people were scared by the attacks of the Mongol and Goryeo army, saying, 'moko kokuri no oni ga kuru (the devils of the Mongol and Goryeo will come)', which phrase later came to represent something scary; thus a tradition spread to the whole country to scare children into obedience by saying 'mukuri kokuri, oni ga kuru'.

During the Muromachi and Sengoku periods in Japan, pirates sailing from Kyushu attacked ships along the coasts of Korea and China and were feared as Japanese pirates (called "wako" in Japanese).

In 1592 and 1598, Toyotomi Hideyoshi, who had unified Japan, ordered daimyōs (feudal lords) all over the nation to the conquest of Ming Dynasty China by way of Korea, after the latter's refusal to allow Japanese forces to march through, while King Seonjo alerting its Chinese counterpart regarding the Japanese threat. Japan completed the occupation of the Korean peninsula in three months. The Korean king Seonjo first relocated to Pyongyang, then Uiju. In 1593, The Ming Chinese emperor intervened and sent his army and recaptured the Korean peninsula. However, the Japanese military were able to gather in Seoul and successfully counterattacked China. Although during the war Korean land forces lost most of their land battles (with only a handful of notable exceptions), the Korean Navy won almost all the naval battles with decisive defeats of the Japanese fleet by Admiral Yi Sun-sin , it managed to cut off Japanese supply lines and helped to stall the invading forces in Korean peninsula. Amid the stagnation of the battle between the Ming army and the Japanese army, Hideyoshi died in September 1598. The Council of Five Elders ordered the remaining Japanese forces in Korea to retreat.

After the war, Japan then initiated a series of policies called Sakoku to isolate itself from international world. It forbade Japanese to go abroad in ships, and initiated the death penalty for Japanese returning to Japan from abroad. This ended Japanese piracy definitively. During the Japanese invasion, much of Korea's cultural heritage was destroyed and looted by the invading Japanese armies. Among the atrocities of the Japanese soldiers was the practice of cutting off noses and ears of slain enemy soldiers, which evolved into cutting off those of the living and the civilians in order to fulfill the "kill quota" assigned to the troops. Hence the origin of the Korean saying to misbehaving children, "Ear and nose cutting devils are coming!".^[25] After the wars, Korean missions were dispatched 11 times to the Tokugawa shogunate of Japan between 1607 and 1811.^[26]

At the end of the 16th century, the Bunroku-Keicho War broke off the relationship between Korea and Japan. However, the Tokugawa shogunate started trading again with Korea by concluding the Treaty of Giyu with the Sō clan of Tsushima Island in 1609, establishing a relationship of near equality through mutual visits of Korean messengers. Tsushinshi were sent from Korea to pay homage to a new shogun or to celebrate the birth of an heir to a shogun. Korean envoys were provided with the same role as an envoy to bring tributes to a Chinese emperor or was used for showing the prestige of Tokugawa shogunate

With the erosion of Qing dynasty influences in the 19th century, Korea began to resist Chinese influence, but also Western and Japanese control. Japan was rapidly modernizing in the second half of the 19th century and showing a keen interest in Korea, especially as it was the closest potential point of expansion directly on the Asian mainland. It was perceived that Japan would be vulnerable to any power that controlled the Korean peninsula. With the Japan–Korea Treaty of 1876, Japan decided the expansion of their settlement, the addition of the market and acquired an enclave in Busan. A severe conflict at court between Heungseon Daewongun, the biological father of Gojong (king of the Joseon Dynasty), and Gojong's wife Empress Myeongseong continued. In 1882, Daewongun was seized by the Qing dynasty troops, and confined in Tianjin City (Jingo Incident). The Min clan including Queen Min assumed authority, but relations between Korea and Japan did not turn better, the Min clan changing their policies from being pro-Japanese to pro-Qing China. In the First Sino-Japanese War, When Japan beat China in 1895, the Treaty of Shimonoseki was concluded, and removed China's suzerainty over Korea.^[27] Korea then gravitated closer to Russia. Japan became alarmed when Russia enhanced its grip and influence over the Korean peninsula by acquiring vital state assets such as the mining rights in Chongsong and Gyeongwon sold off by Queen Min, such as timber rights in the north, and tariff rights, so it purchased back and restored many of these. Japan victory against China in the First Sino-Japanese War, released Korea from China's tributary system and the Treaty of Shimonoseki forced it to acknowledge Korea as an "independent" nation. Japan encouraged the modernization of Korea, however, the Min clan, including the Queen Min, start to take conspire against the rise of Japanese power in Korea.^[28] In 1895, Queen Min was assassinated by Japan after seeking to promote Russian influence and oppose reform.^[29]

In 1897, Joseon was renamed the Korean Empire (1897–1910), affirming its independence, but greatly gravitated closer to Russia, with the King ruling from the Russian legation, and then using Russian guards upon return to his palace. Japan declared war on Russia to drive out Russian influence, while Korea declared to be neutral. Japan's victory in the Russo-Japanese War, the Japan–Korea Treaty of 1905 was agreed in which Korea became a protectorate of Japan, a precursor to its annexation. Emperor Gojong, who did not accept the conclusion of this Treaty, dispatched secret envoys to the second Hague Peace Conference in 1907 in order to denounce the conclusion of the treaty as compulsive and invalid, but the trial failed and the Korea-Japan relationship deteriorated. On July 24, they concluded the Japan–Korea Treaty of 1907 to grasp domestic administration authority, and disbanded the army of the Korean Empire on August 1 immediately after that. Itō Hirobumi, who was the first prime minister of Japan and one of the elder statesmen, was then leading the preparation process of annexation as Resident-General of Korea. In 1909, Ito Hirobumi was assassinated by An Jung-geun. On August 22, 1910, Japan officially annexed the Korean Empire by signing the Japan-Korea Annexation Treaty.^[30]

During the colonial period, more than 100,000 Koreans served in the Imperial Japanese Army. The service of these Korean men was forced upon them,^[31] but it is without a doubt that Koreans fought alongside Japanese as allies to battle against the forces of the Allies of World War II.^[32] Some Korean women were also sent as comfort women at the war front to serve the Imperial Japanese Army.^[33][34][35] There are several controversies about this issue, including the veracity on the nature of the comfort women as sex slaves, or whether the Japanese Imperial Army was involved in the supposed women's abductions.^[36] The issue on comfort women had been the source of diplomatic tensions between Japan and Korea since the 1980s.

Kim Il-sung led a Korean independence movement, which was active in the border areas of China and Russia, particularly in areas with considerable ethnic Korean populations. Kim founded North Korea, and his descendants have still not signed a peace treaty with Japan. The Provisional Government of the Republic of Korea, led by (later) South Korea's first president Syngman Rhee, moved from Shanghai to Chongqing. Lee lobbied in the United States and was recognized by the South Korean administrator by Douglas MacArthur.^[37] Japanese control of Korea ended on September 9, 1945 when the Japanese Governor-General of Korea signed the surrender document of the United States in Seoul.

At the end of World War II, Korea regained its independence after 35 years of imperialist Japanese rule. Per the Yalta Conference agreements, Soviet forces accepted surrender of Japanese forces in northern Korea above the 38th parallel, and U.S. forces south of that line. Korea was then divided into Soviet (North Korean) and U.S. (South Korean) spheres. South Korea refused diplomatic and trade relations with Japan, using tensions with Japan to rally support for the South Korean government. The early ROK (Republic of Korea; South Korea) government derived its legitimacy from its opposition to Japan and North Korea, portraying South Korea as under threat from the North and South. The diplomatic relationship between Japan and South Korea was established in 1965, when the Treaty on Basic Relations was signed; Japan subsequently recognized the Republic of Korea (the official name of South Korea) as the only legitimate government on the Korean Peninsula. As such, North Korea does not have official diplomatic ties with Japan.

In recent years, the two nations jointly hosted the 2002 FIFA World Cup, and (South) Korean pop culture experienced major popularity in Japan, a phenomenon dubbed the "Korean Wave" (韓流) in Japan. The Korean Wave has sparked a fad for Korean movies, dramas and popular music in Japan. In return, certain Japanese pop culture productions like anime, manga and video games gained significant popularity in South Korea.

In 2015, relations between the two nations reached a high point when South Korea and Japan addressed the issue of comfort women, or sex slaves, used by Japanese military during World War II. Fumio Kishida, the Japanese Foreign Minister, pledged that the Japanese government would donate 1 billion yen ($8.3 million USD, 2015) to help pay for the care of the surviving former sex slaves. Furthermore, Japanese Prime Minister, Shinzō Abe, made public apologies to the "women who underwent immeasurable and painful experiences and suffered insurable physical and psychological wounds as comfort women". Former South Korean president, Park Geun-hye, without any communication with the alive “comfort women”, hailed this deal as a sign of positive progression in Japanese and South Korean relations.^[38][39]