The military history of Japan is characterized by a long period of feudal wars, followed by domestic stability, and then rampant imperialism. It culminates with Japan's defeat by the Allies in World War II. Since then, Japan's constitution has prohibited the use of military force to wage war against other nations.

Unless one counts the Allied occupation following World War II, the Japanese main islands have never been successfully invaded in recorded history.

Recent archaeological research has uncovered traces of wars as far back as the Jōmon period (ca. 10,000–300 BC) between the various tribes existing on the Japanese Archipelago. Some theorists believe that shortly after the Yayoi period (ca. 300 BC – 250 AD) horse riders from the Korean Peninsula invaded southern Kyūshū, then spread to all the way to northern Honshū. This is when horse-riding and iron tools were first introduced to the islands.

Near the end of the Jōmon period (ca. 300 BC), villages and towns became surrounded by moats and wooden fences due to increasing violence within or between communities. Some remains were found with head and arrow injuries. Battles were fought with weapons like the sword, sling, spear, and bow and arrow.

The history of Japan encompasses the history of the islands of Japan and the Japanese people, spanning the ancient history of the region to the modern history of Japan as a nation state. Following the last ice age, around 12,000 BC, the rich ecosystem of the Japanese Archipelago fostered human development. The earliest-known pottery belongs to the Jōmon period. The first known written reference to Japan is in the brief information given in Twenty-Four Histories in the 1st century AD. The main cultural and religious influences came from China.

The first permanent capital was founded at Nara in 710 AD, which became a center of Buddhist art, religion and culture. The current imperial family emerged about 700 AD, but until 1868 (with few exceptions) had high prestige but little power. By 1550 or so political power was subdivided into several hundred local units, or "domains" controlled by local "daimyō" (lords), each with his own force of samurai warriors. Tokugawa Ieyasu came to power in 1600, gave land to his supporters, set up his "bakufu" (military government) at Edo (modern Tokyo). The "Tokugawa period" was prosperous and peaceful, but Japan deliberately terminated the Christian missions and cut off almost all contact with the outside world. In the 1860s the Meiji Period began, and the new national leadership systematically ended feudalism and transformed an isolated, underdeveloped island country into a world power that closely followed Western models. Democracy was problematic, because Japan's powerful military was semi-independent and overruled—or assassinated—civilians in the 1920s and 1930s. The military moved into China starting in 1931 but was defeated in the Pacific War by the United States and Britain.

Japan ⁱ/dʒəˈpæn/ (Japanese: 日本 Nihon or Nippon; formally 日本国  Nippon-koku or Nihon-koku, literally the State of Japan) is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south. The characters that make up Japan's name mean "sun-origin", which is why Japan is sometimes referred to as the "Land of the Rising Sun".

Japan is an archipelago of 6,852 islands. The four largest islands are Honshū, Hokkaidō, Kyūshū and Shikoku, together accounting for ninety-seven percent of Japan's land area. Japan has the world's tenth-largest population, with over 127 million people. The Greater Tokyo Area, which includes the de facto capital city of Tokyo and several surrounding prefectures, is the largest metropolitan area in the world, with over 30 million residents.

Archaeological research indicates that people lived in Japan as early as the Upper Paleolithic period. The first written mention of Japan is in Chinese history texts from the 1st century AD. Influence from other nations followed by long periods of isolation has characterized Japan's history. In the late 19th and early 20th centuries, victory in the First Sino-Japanese War, the Russo-Japanese War and World War I allowed Japan to expand its empire during a period of increasing militarism. The Second Sino-Japanese War of 1937 expanded into part of World War II in 1941, which came to an end in 1945 following the atomic bombings of Hiroshima and Nagasaki. Since adopting its revised constitution in 1947, Japan has maintained a unitary constitutional monarchy with an emperor and an elected parliament called the Diet.

Military history is a humanities discipline within the scope of general historical recording of armed conflict in the history of humanity, and its impact on the societies, their cultures, economies and changing intra and international relationships.

Professional historians normally focus on military affairs that had a major impact on the societies involved as well as the aftermath of conflicts, while amateur historians and hobbyists often take a larger interest in the details of battles, equipment and uniforms in use.

The essential subjects of military history study are the causes of war, the social and cultural foundations, military doctrine on each side, the logistics, leadership, technology, strategy, and tactics used, and how these changed over time.

As an applied field, military history has been studied at academies and service schools because the military command seeks to not repeat past mistakes, and improve upon its current performance by instilling an ability in commanders to perceive historical parallels during a battle, so as to capitalize on the lessons learned from the past.

The Japanese people (日本人, Nihonjin, Nipponjin^?) are a nationality originating in the Japanese archipelago and are the predominant ethnic group of Japan. Worldwide, approximately 130 million people are of Japanese descent; of these, approximately 127 million are residents of Japan. People of Japanese ancestry who live in other countries are referred to as nikkeijin (日系人^?). The term ethnic Japanese may also be used in some contexts to refer to a locus of ethnic groups including the Yamato, Ainu and Ryukyuan people.

The Japanese language is a Japonic language that is sometimes treated as a language isolate; it is also related to the Ryukyuan languages, and both are suggested to be part of the proposed Altaic language family. The Japanese language has a tripartite writing system using Hiragana, Katakana, and Kanji. Domestic Japanese people use primarily Japanese for daily interaction. The adult literacy rate in Japan exceeds 99%.

Japanese religion has traditionally been syncretic in nature, combining elements of Buddhism and Shinto. Shinto, a polytheistic religion with no book of religious canon, is Japan's native religion. Shinto was one of the traditional grounds for the right to the throne of the Japanese imperial family, and was codified as the state religion in 1868 (State Shinto was abolished by the American occupation in 1945). Mahayana Buddhism came to Japan in the sixth century and evolved into many different sects. Today the largest form of Buddhism among Japanese people is the Jōdo Shinshū sect founded by Shinran.^{[citation needed]}