The history of Japanese foreign relations deals with the international relations in terms of diplomacy, economics and political affairs from about 1850 to 2000. The kingdom was largely isolated before the 1850s, with limited contacts through Dutch traders. The Meiji Restoration was a political revolution that installed a new leadership that was eager to borrow Western technology and organization. The government in Tokyo carefully monitored and controlled outside interactions. Japanese delegations to Europe brought back European standards which were widely imposed across the government and the economy. Trade flourished, and Japan rapidly industrialized. In the late 19th century Japan defeated China, and acquired numerous colonies, including Formosa and Okinawa. The rapid advances in Japanese military prowess led to the Russo-Japanese War, the first time a non-Western nation defeated a European power. Imperialism continued as it took control of Korea, and began moving into Manchuria. Its only military alliance was with Great Britain, from 1902 to 1923. In the First World War, it joined the Entente powers, and seized many German possessions in the Pacific and in China.

Although the political system was officially democratic, the Army increasingly seized control in Japan. In the 1920s, Japan contested Manchuria with the Soviet Union, invading it in 1931. It joined the Axis alliance with Germany, but there was little close cooperation between the two nations until 1943. Japan opened a full-scale war in China in 1937, committing several war crimes. Two puppet regimes were nominally in charge in China and Manchuria. Military confrontations with the Soviet Union led Japan to sign a Neutrality Pact with the Soviet union. American, British, and Dutch economic and financial pressures resulted in the cut off of vitally needed oil supplies in 1941. Japan declared war, and in three months won multiple battles, as well as continuing the war with China. The Japanese economy could not support the large-scale war effort, especially with the rapid buildup of the American navy. By 1944, Japan was heavily on the defensive, as its Greater East Asia Co-prosperity Sphere collapsed, its navy was sunk, and American bombing started to devastate major Japanese cities. Japan surrendered following the atomic bombings of Hiroshima and Nagasaki and Soviet invasion of Manchuria.

Japan was a very minor player in international affairs in the late 1940s, but its economy revived in part as a supply base for the Korean War. Non-involvement became the central focus of Japanese foreign policy, together with very rapid growth of its industrial exports. It retains very close relations with the United States, which provides it with military protection. South Korea, China, and other countries in the Western Pacific trade on a very large scale with Japan.

After the United States, China and Japan have the two largest economies in the 21st century world. In 2008, China-Japan trade reached $266 billion, making them the top trading partners. However, historical issues, including Japanese war crimes and maritime disputes, have created tensions. Despite this, leaders from both countries have made efforts to improve their relations. In 2021, Japan hosted the Summer Olympics. Following the Russian invasion of Ukraine in 2022, Japan condemned it and implemented sanctions, including freezing assets and banning new investments and exports of high-tech goods. The conflict in Ukraine, along with threats from China and North Korea, led to a shift in Japan's security policy. Japan increased defense spending and announced a major shift in military policy, acquiring counterstrike capabilities and aiming to increase the defense budget to 2% of GDP by 2027.

Beginning with the Meiji Restoration of 1868, which established a new, centralized regime, Japan set out to "gather wisdom from all over the world" and embarked on an ambitious program of military, social, political, and economic reforms that transformed it within a generation into a modern nation-state and major world power. The Meiji oligarchy was aware of Western progress, and "learning missions" were sent abroad to absorb as much of it as possible. The Iwakura Mission, the most important one, was led by Iwakura Tomomi, Kido Takayoshi and Ōkubo Toshimichi, contained forty-eight members in total and spent two years (1871–73) touring the United States and Europe, studying every aspect of modern nations, such as government institutions, courts, prison systems, schools, the import-export business, factories, shipyards, glass plants, mines, and other enterprises. Upon returning, mission members called for domestic reforms that would help Japan catch up with the West.

European powers imposed a series of "unequal treaties" in the 1850s and 1860s that gave privileged roles to their nationals in specially designated treaty ports. Representative was the 1858 Treaty of Amity and Commerce with the United States, also called the "Harris Treaty." It opened the ports of Kanagawa and four other Japanese cities to trade, and provided for the exchange of diplomats. It granted extraterritoriality to foreigners, so that they governed themselves and were not under the control of Japanese courts or authorities. There were numerous trading stipulations favorable to the Americans. The Dutch, British and Russians quickly followed suit with their own treaties, backed up by their own powerful naval forces. The unequal treaties were part of the series imposed on non-Western countries, such as Persia 1857, Turkey 1861, Siam 1855, and China 1858. The inequality was not quite as severe as suffered by these other countries, but it rankled so much that ending the inequality became a priority that was finally achieved in the 1890s. The humiliation was not as bad as China suffered, but it energized anti-foreign forces inside Japan. On the other hand, the new treaties, provided for tariffs on imports from Europe; imports multiplied by a factor of nine between 1860 and 1864, and the tariff revenue provided major financial backing for the Meiji regime. Exports of tea, silk and other Japanese products multiplied by a factor of four in four years, dramatically stimulating the local economy while causing galloping inflation that drove up the price of rice. The Meiji leaders sketched a new vision for a modernized Japan's leadership role in Asia, but they realized that this role required that Japan develop its national strength, cultivate Japanese nationalism among the population, and carefully craft policies toward potential enemies. The skills and tricks of negotiation had to be learned, so they could compete on an equal basis with experienced Western diplomats. No longer could Westerners be seen as "barbarians"; In time, Japan formed a corps of professional diplomats and negotiators.

Starting in the 1860s Japan rapidly modernized along Western lines, adding industry, bureaucracy, institutions and military capabilities that provided the base for imperial expansion into Korea, China, Taiwan and islands to the south. It saw itself vulnerable to aggressive Western imperialism unless it took control of neighboring areas. It took control of Okinawa and Formosa. Japan's desire to control Taiwan, Korea and Manchuria, led to the first Sino-Japanese War with China in 1894–1895 and the Russo-Japanese War with Russia in 1904–1905. The war with China made Japan the world's first Eastern, modern imperial power, and the war with Russia proved that a Western power could be defeated by an Eastern state. The aftermath of these two wars left Japan the dominant power in the Far East with a sphere of influence extending over southern Manchuria and Korea, which was formally annexed as part of the Japanese Empire in 1910.

Okinawa island is the largest of the Ryukyu Islands, and paid tribute to China from the late 14th century. Japan took control of the entire Ryukyu island chain in 1609 and formally incorporated it into Japan in 1879.