Sea of Japan in the context of Niigata, Niigata

Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asian mainland, it is bordered to the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea in the south. The Japanese archipelago consists of four major islands alongside 14,121 smaller islands. Japan is divided into 47 administrative prefectures and eight traditional regions, and around 75% of its terrain is mountainous and heavily forested, concentrating its agriculture and highly urbanized population along its eastern coastal plains. With a population of over 123 million as of 2025, it is the world's 11th most populous country. Tokyo is the country's capital and largest city.

The first known habitation of the archipelago dates to the Upper Paleolithic, with the beginning of the Japanese Paleolithic dating to c. 36,000 BC. Between the 4th and 6th centuries, its kingdoms were united under an emperor in Nara and later Heian-kyō. From the 12th century, actual power was held by military aristocrats known as shōgun and feudal lords called daimyō, enforced by warrior nobility named samurai. After rule by the Kamakura and Ashikaga shogunates and a century of warring states, Japan was unified in 1600 by the Tokugawa shogunate, which implemented an isolationist foreign policy. In 1853, an American fleet forced Japan to open trade to the West, which led to the end of the shogunate and the restoration of imperial power in 1868.

Honshu (Japanese: 本州, Hepburn: Honshū; pronounced [hoꜜɰ̃.ɕɯː] ; lit. 'main province'), historically known as Akitsushima (秋津島; lit. 'dragonfly island'), is the largest of Japan's four main islands. It lies between the Pacific Ocean (east) and the Sea of Japan (west). It is the seventh-largest island in the world, and the second-most populous after the Indonesian island of Java.

Honshu had a population of 104 million as of 2017, constituting 81.3% of the entire population of Japan, and mostly concentrated in the coastal areas and plains. Approximately 30% of the total population resides in the Greater Tokyo Area on the Kantō Plain. As the historical center of Japanese cultural and political power, the island includes several past Japanese capitals, including Kyoto, Nara, and Kamakura. Much of the island's southern shore forms part of the Taiheiyō Belt, a megalopolis that spans several of the Japanese islands. Honshu also contains Japan's highest mountain, Mount Fuji, and its largest lake, Lake Biwa.

The Mongol Empire was the largest contiguous empire in history. Originating in present-day Mongolia in East Asia, the empire at its height stretched from the Sea of Japan to Eastern Europe, extending northward into Siberia and east and southward into the Indian subcontinent, mounting invasions of Southeast Asia, and conquering the Iranian plateau; and reaching westward as far as the Levant and the Carpathian Mountains.

The empire emerged from the unification of several nomadic tribes in the Mongol heartland under the leadership of Temüjin, known by the title of Genghis Khan (c. 1162–1227), whom a council proclaimed as the ruler of all Mongols in 1206. The empire grew rapidly under his rule and that of his descendants, who sent out invading armies in every direction. The vast transcontinental empire connected the East with the West, and the Pacific to the Mediterranean, in an enforced Pax Mongolica, allowing the exchange of trade, technologies, commodities, and ideologies across Eurasia.

The Chūbu region (中部地方, Chūbu-chihō), Central region, or Central Japan (中部日本, Chūbu-nihon) is a large and diverse region in the middle of Honshū, Japan's main island. In a wide, classical definition, it encompasses nine prefectures (ken): Aichi, Fukui, Gifu, Ishikawa, Nagano, Niigata, Shizuoka, Toyama, and Yamanashi.

It is located directly between the Kantō region and the Kansai region and includes the major city of Nagoya as well as Pacific Ocean and Sea of Japan coastlines, extensive mountain resorts, and Mount Fuji.

Kyoto Prefecture (京都府, Kyōto-fu; Japanese pronunciation: [kʲoꜜː.to, kʲoː.toꜜ.ɸɯ]) is a prefecture of Japan located in the Kansai region of Honshu. Kyoto Prefecture has a population of 2.58 million and has a geographic area of 4,612 square kilometres (1,781 sq mi). Kyoto Prefecture borders Fukui Prefecture to the northeast, Shiga Prefecture to the east, Mie Prefecture to the southeast, Nara Prefecture and Osaka Prefecture to the south, and Hyōgo Prefecture to the west.

Kyoto, the capital and largest city, accommodates 57% of the prefecture's total population, with other major cities including Uji, Kameoka, and Maizuru. Kyoto Prefecture is located on the Sea of Japan coast and extends to the southeast towards the Kii Peninsula, covering territory of the former provinces of Yamashiro, Tamba, and Tango. Kyoto Prefecture is centered on the historic Imperial capital of Kyoto, and is one of Japan's two "prefectures" using the designation fu rather than the standard ken for prefectures. Kyoto has made Kyoto Prefecture one of the most popular tourism destinations in Japan for national and international tourists, and 21% of the prefecture's land area was designated as Natural Parks. Kyoto Prefecture forms part of the Keihanshin metropolitan area, the second-most-populated region in Japan after the Greater Tokyo area and one of the world's most productive regions by GDP.

North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korean Peninsula and borders China and Russia to the north at the Yalu (Amnok) and Tumen rivers, and South Korea to the south at the Korean Demilitarized Zone (DMZ). The country's western border is formed by the Yellow Sea, while its eastern border is defined by the Sea of Japan. North Korea, like South Korea, claims to be the sole legitimate government of the Korean Peninsula and adjacent islands. Pyongyang is the capital and largest city.

The Korean Peninsula was first inhabited as early as the Lower Paleolithic period. Its first kingdom was noted in Chinese records in the early 7th century BCE. Following the unification of the Three Kingdoms of Korea into Silla and Balhae in the late 7th century, Korea was ruled by the Goryeo dynasty (918–1392) and the Joseon dynasty (1392–1897). The succeeding Korean Empire (1897–1910) was annexed in 1910 into the Empire of Japan. In 1945, after the Japanese surrender at the end of World War II, Korea was divided into two zones along the 38th parallel, with the north occupied by the Soviet Union and the south occupied by the United States. In 1948, separate governments were formed in Korea: the socialist and Soviet-aligned Democratic People's Republic of Korea in the north, and the capitalist, Western-aligned Republic of Korea in the south. The North Korean invasion of South Korea in 1950 started the Korean War. In 1953, the Korean Armistice Agreement brought about a ceasefire and established a demilitarized zone (DMZ), but no formal peace treaty has ever been signed. Post-war North Korea benefited greatly from economic aid and expertise provided by other Eastern Bloc countries. However, Kim Il Sung, North Korea's first leader, promoted his personal philosophy of Juche as the state ideology. Pyongyang's international isolation sharply accelerated from the 1980s onwards as the Cold War came to an end. The fall of the Soviet Union in 1991 then brought about a sharp decline to the North Korean economy. From 1994 to 1998, North Korea suffered a famine with the population continuing to suffer from malnutrition. In 2024, the DPRK formally abandoned efforts to reunify Korea.

South Korea, officially the Republic of Korea (ROK), is a country in East Asia. It constitutes the southern half of the Korean Peninsula and borders North Korea along the Korean Demilitarized Zone, with the Yellow Sea to the west and the Sea of Japan to the east. Like North Korea, South Korea claims to be the sole legitimate government of the entire peninsula and adjacent islands. It has a population of about 52 million, of which half live in the Seoul metropolitan area, the ninth most populous metropolitan area in the world; other major cities include Busan, Daegu, and Incheon.

The Korean Peninsula was inhabited as early as the Lower Paleolithic period. Its first kingdom was noted in Chinese records in the early seventh century BC. From the mid first century BC, various polities consolidated into the rival kingdoms of Goguryeo, Baekje, and Silla. The lattermost eventually unified most of the peninsula for the first time in the late seventh century AD, while Balhae succeeded Goguryeo in the north. The Goryeo dynasty (918–1392) achieved lasting unification and established the basis for the modern Korean identity. The subsequent Joseon dynasty (1392–1897) generated cultural, economic, and scientific achievements and also established isolationism starting from the mid-17th century. The succeeding Korean Empire (1897–1910) sought modernization and reform but was annexed in 1910 into the Empire of Japan. Japanese rule ended following Japan's surrender in World War II, after which Korea was divided into two zones: the Soviet-occupied northern zone and the United States-occupied southern zone. After negotiations on reunification failed, the southern zone became the Republic of Korea in August 1948, while the northern zone became the communist Democratic People's Republic of Korea the following month.

Sakhalin (Russian: Сахалин, IPA: [səxɐˈlʲin]) is an island in Northeast Asia. Its north coast lies 6.5 km (4.0 mi) off the southeastern coast of Khabarovsk Krai in Russia, while its southern tip lies 40 kilometres (25 mi) north of the Japanese island of Hokkaido. An island of the West Pacific, Sakhalin divides the Sea of Okhotsk to its east from the Sea of Japan to its southwest. It is administered as part of Sakhalin Oblast and is the largest island of Russia, with an area of 72,492 square kilometres (27,989 sq mi). The island has a population of roughly 500,000, the majority of whom are Russians. The indigenous peoples of the island are the Ainu, Oroks, and Nivkhs, who are now present in very small numbers.

The island's name is derived from the Manchu word Sahaliyan (ᠰᠠᡥᠠᠯᡳᠶᠠᠨ), which was the name of the Qing dynasty city of Aigun. The Ainu people of Sakhalin paid tribute to the Yuan, Ming, and Qing dynasties and accepted official appointments from them. Sometimes the relationship was forced but control from dynasties in China was loose for the most part.

The Qing dynasty (/tʃɪŋ/ CHING), officially the Great Qing, was a Manchu-led imperial dynasty of China and an early modern empire in East Asia. The last imperial dynasty in Chinese history, the Qing dynasty was preceded by the Ming dynasty and succeeded by the Republic of China. At its height of power, the empire stretched from the Sea of Japan in the east to the Pamir Mountains in the west, and from the Mongolian Plateau in the north to the South China Sea in the south. Originally emerging from the Later Jin dynasty founded in 1616 and proclaimed in Shenyang in 1636, the dynasty seized control of the Ming capital Beijing and North China in 1644, traditionally considered the start of the dynasty's rule. The dynasty lasted until the Xinhai Revolution of October 1911 led to the abdication of the last emperor in February 1912. The multi-ethnic Qing dynasty assembled the territorial base for modern China. The Qing controlled the most territory of any dynasty in Chinese history, and in 1790 represented the fourth-largest empire in world history to that point. With over 426 million citizens in 1907, it was the most populous country at the time.

Nurhaci, leader of the Jianzhou Jurchens and House of Aisin-Gioro who was also a vassal of the Ming dynasty, unified Jurchen clans (known later as Manchus) and founded the Later Jin dynasty in 1616, renouncing the Ming overlordship. As the founding Khan of the Manchu state he established the Eight Banners military system, and his son Hong Taiji was declared Emperor of the Great Qing in 1636. As Ming control disintegrated, peasant rebels captured Beijing as the short-lived Shun dynasty, but the Ming general Wu Sangui opened the Shanhai Pass to the Qing army, which defeated the rebels, seized the capital, and took over the government in 1644 under the Shunzhi Emperor and his prince regent. While the Qing became a Chinese empire, resistance from Ming rump regimes and the Revolt of the Three Feudatories delayed the complete conquest until 1683, which marked the beginning of the High Qing era. As an emperor of Manchu ethnic origin, the Kangxi Emperor (1661–1722) consolidated control, relished the role of a Confucian ruler, patronised Buddhism, encouraged scholarship, population and economic growth.

Hyōgo Prefecture (兵庫県, Hyōgo-ken; Japanese pronunciation: [çoꜜː.ɡo, -ŋo, çoː.ɡoꜜ.keɴ, -ŋoꜜ.keɴ]) is a prefecture of Japan located in the Kansai region of Honshu. Hyōgo Prefecture has a population of 5,469,762 (as of 1 June 2019) and a geographic area of 8,400 square kilometres (3,200 square miles). Hyōgo Prefecture borders Kyoto Prefecture to the east, Osaka Prefecture to the southeast, and Okayama and Tottori prefectures to the west.

Kobe is the capital and largest city of Hyōgo Prefecture, and the seventh-largest city in Japan, with other major cities including Himeji, Nishinomiya, and Amagasaki. Hyōgo Prefecture's mainland stretches from the Sea of Japan to the Seto Inland Sea, where Awaji Island and a small archipelago of islands belonging to the prefecture are located. Hyōgo Prefecture is a major economic center, transportation hub, and tourist destination in western Japan, with 20% of the prefecture's land area designated as Natural Parks. Hyōgo Prefecture forms part of the Kobe metropolitan area and Osaka metropolitan area, the second-most-populated urban region in Japan after the Greater Tokyo area and one of the world's most productive regions by GDP.

The Mongol heartland or Mongolian heartland is the contiguous geographical area in which the Mongol people have primarily lived, particularly as a historiographic term. It is generally considered to comprise the Mongolian Plateau and some adjacent territories, although its exact extent has been changing over the course of history—particularly since the rise of the Mongol Empire in the 13th century. The area is also described as the heartland of the Mongol Empire during its greatest extent, when it stretched from the Sea of Japan in the east to the Middle East and Eastern Europe in the west, making it the largest contiguous land empire in human history.

The modern area that the Mongols live in approximately includes: the modern state of Mongolia; the Inner Mongolia Autonomous Region, along with Dzungaria in Xinjiang and parts of Manchuria, Qinghai, and Ningxia in China; as well as the Buryatia Republic and a few smaller territories in Russia. The Mongolic peoples in this area share the common traditional Mongol culture as well as the Mongol language to varying levels. With the exception of the Mongolian state, all areas in the Mongol heartland have non-Mongol majorities.

The Russo-Japanese War (8 February 1904 – 5 September 1905) was fought between the Russian Empire and the Empire of Japan over rival imperial ambitions in Manchuria and the Korean Empire. The major land battles of the war were fought on the Liaodong Peninsula and near Mukden in Southern Manchuria, with naval battles taking place in the Yellow Sea and the Sea of Japan.

Russia had pursued an expansionist policy in Siberia and the Far East since the reign of Ivan the Terrible in the 16th century. At the end of the First Sino-Japanese War, the Treaty of Shimonoseki of 1895 had ceded the Liaodong Peninsula and Port Arthur to Japan before the Triple Intervention, in which Russia, Germany, and France forced Japan to relinquish its claim. Japan feared that Russia would impede its plans to establish a sphere of influence in mainland Asia, especially as Russia built the Trans-Siberian Railroad, began making inroads in Korea, and acquired a lease of the Liaodong Peninsula and Port Arthur from China in 1898. Japan signed the Anglo-Japanese Alliance in 1902, and began offering to recognize Russia's dominance in Manchuria in exchange for recognition of Korea as part of Japan's sphere of influence. However, this was rejected by Russia.

Niigata Prefecture (新潟県, Niigata-ken; Japanese pronunciation: [ɲiː.ɡa.ta, -taꜜ.keɴ, ɲiː.ŋa-]) is a prefecture in the Chūbu region of Honshu of Japan. Niigata Prefecture has a population of 2071066 (1 October,2025) and is the fifth-largest prefecture of Japan by geographic area at 12,584.18 km (4,858.78 sq mi). Niigata Prefecture borders Toyama Prefecture and Nagano Prefecture to the southwest, Gunma Prefecture to the south, Fukushima Prefecture to the east, and Yamagata Prefecture to the northeast.

Niigata is the capital and largest city of Niigata Prefecture, with other major cities including Nagaoka, Jōetsu, and Sanjō. Niigata Prefecture contains the Niigata Major Metropolitan Area centered on Niigata with a population of 1,395,612, the largest metropolitan area on the Sea of Japan coast and the twelfth-largest in Japan. Niigata Prefecture is part of the historic Hokuriku region and features Sado Island, the sixth largest island of Japan in area following the four main islands and Okinawa Island.

Fukui Prefecture (福井県, Fukui-ken; Japanese pronunciation: [ɸɯ̥.kɯ(ꜜ)(.)i, -kɯ.iꜜ.keɴ, -kɯꜜi.keɴ]) is a prefecture of Japan located in the Chūbu region of Honshū. Fukui Prefecture has a population of 737,229 (1 January 2025) and has a geographic area of 4,190 km (1,617 sq mi). Fukui Prefecture borders Ishikawa Prefecture to the north, Gifu Prefecture to the east, Shiga Prefecture to the south, and Kyoto Prefecture to the southwest.

Fukui is the capital and largest city of Fukui Prefecture, with other major cities including Sakai, Echizen, and Sabae. Fukui Prefecture is located on the Sea of Japan coast and is part of the historic Hokuriku region of Japan. The Matsudaira clan, a powerful samurai clan during the Edo period that became a component of the Japanese nobility after the Meiji Restoration, was headquartered at Fukui Castle on the site of the modern prefectural offices. Fukui Prefecture is home to the Kitadani Formation and Kitadani Family, the Ichijōdani Asakura Family Historic Ruins, and the Tōjinbō cliff range.

Ishikawa Prefecture (石川県, Ishikawa-ken; Japanese pronunciation: [i.ɕi̥.ka.wa, -waꜜ.keɴ]) is a prefecture of Japan located in the Chūbu region of Honshu island. Ishikawa Prefecture has a population of 1,096,721 (1 January 2025) and has a geographic area of 4,191 km (1618 sq mi). Ishikawa Prefecture borders Toyama Prefecture to the east, Gifu Prefecture to the southeast, and Fukui Prefecture to the south.

Kanazawa is the capital and largest city of Ishikawa Prefecture, with other major cities including Hakusan, Komatsu, and Kaga. Ishikawa is located on the Sea of Japan coast and features most of the Noto Peninsula which forms Toyama Bay, one of the largest bays in Japan. Ishikawa Prefecture is part of the historic Hokuriku region and formerly an important populated center that contained some of the wealthiest han (domains) of the Japanese feudal era. Ishikawa Prefecture is home to Kanazawa Castle, Kenroku-en one of the Three Great Gardens of Japan, Nyotaimori ("body sushi"), and Kutani ware.

The Tsugaru Strait (津軽海峡, Tsugaru Kaikyō) is a strait between Honshu and Hokkaido in northern Japan connecting the Sea of Japan with the Pacific Ocean. It was named after the western part of Aomori Prefecture. The Seikan Tunnel passes under it at its narrowest point 12.1 miles (19.5 km) between Tappi Misaki on the Tsugaru Peninsula in Aomori Prefecture, Honshu, and Shirakami Misaki on the Matsumae Peninsula in Hokkaido.

Western maps made prior to the 20th century also referred to this waterway as the Strait of Sangar.

The Seto Inland Sea (瀬戸内海, Seto Naikai), sometimes shortened to the Inland Sea, is the body of water separating Honshu, Shikoku, and Kyushu, three of the four main islands of Japan. It serves as a waterway connecting the Pacific Ocean to the Sea of Japan. It connects to Osaka Bay and provides a sea transport link to industrial centers in the Kansai region, including Osaka and Kobe. Before the construction of the San'yō Main Line, it was the main transportation link between Kansai and Kyūshū.

Yamaguchi, Hiroshima, Okayama, Hyōgo, Osaka, Wakayama, Kagawa, Ehime, Tokushima, Fukuoka, and Ōita prefectures have coastlines on the Seto Inland Sea; the cities of Hiroshima, Iwakuni, Takamatsu, and Matsuyama are also located on it.