Jeju Island in the context of "Korea"

The East China Sea is a marginal sea of the Western Pacific Ocean, located directly offshore from East China. China names the body of water along its eastern coast as "East Sea" (Dōng Hǎi, simplified Chinese: 东海; traditional Chinese: 東海) due to direction, the name of "East China Sea" is otherwise designated as a formal name by International Hydrographic Organization (IHO) and used internationally.

It covers an area of roughly 1,249,000 square kilometers (482,000 sq mi). The sea's northern extension between Korean Peninsula and mainland China is the Yellow Sea, separated by an imaginary line between the southwestern tip of South Korea's Jeju Island and the eastern tip of Qidong at the Yangtze River estuary.

Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in Asia in 1945, it has been politically divided at or near the 38th parallel between North Korea (Democratic People's Republic of Korea; DPRK) and South Korea (Republic of Korea; ROK). Both countries proclaimed independence in 1948, and the two countries fought the Korean War from 1950 to 1953. The region is bordered by China to the north and Russia to the northeast, across the Amnok (Yalu) and Duman (Tumen) rivers, and is separated from Japan to the southeast by the Korea Strait.

Known human habitation of the Korean peninsula dates to 40,000 BC. The kingdom of Gojoseon, which according to tradition was founded in 2333 BC, fell to the Han dynasty in 108 BC. It was followed by the Three Kingdoms period, in which Korea was divided into Goguryeo, Baekje, and Silla. In 668 AD, Silla conquered Baekje and Goguryeo with the aid of the Tang dynasty, forming Unified Silla; Balhae succeeded Goguryeo in the north. In the late 9th century, Unified Silla collapsed into three states, beginning the Later Three Kingdoms period. In 918, Goguryeo was resurrected as Goryeo, which achieved what has been called a "true national unification" by Korean historians, as it unified both the Later Three Kingdoms and the ruling class of Balhae after its fall. Goryeo, whose name developed into the modern exonym "Korea", was highly cultured and saw the invention of the first metal movable type. During the 13th century, Goryeo became a vassal state of the Mongol Empire. Goryeo overthrew Mongol rule before falling to a coup led by General Yi Seong-gye, who established the Joseon dynasty in 1392. The first 200 years of Joseon were marked by peace; the Hangul, the Korean alphabet was created and Confucianism became influential. This ended with Japanese and Qing invasions, which brought devastation to Joseon and led to Korean isolationism. After the invasions, an isolated Joseon experienced another nearly 200-year period of peace and prosperity, along with cultural and technological development. In the final years of the 19th century, Japan forced Joseon to open up and Joseon experienced turmoil such as the Kapsin Coup, Donghak Peasant Revolution, and the assassination of Empress Myeongseong. In 1895, Japan defeated China in the First Sino-Japanese War and China lost suzerainty over Korea and Korea was placed under further Japanese influence. In 1897, the centuries old Joseon was replaced by the Korean Empire with the Joseon's last king, Gojong, becoming the Emperor of the Korean Empire. Japan's further victory in the 1904–1905 Russo-Japanese War, expelled Russian influence in Korea and Manchuria. In 1905, the Korean Empire became a protectorate of the Empire of Japan. In 1910, the Empire of Japan officially annexed the Korean peninsula.

Korean is the native language for about 81 million people, mostly of Korean descent. It is the national language of both North Korea and South Korea. In the south, the language is known as Hangugeo (South Korean: 한국어) and in the north, it is known as Chosŏnŏ (North Korean: 조선어). Since the turn of the 21st century, Korean popular culture have spread around the world through globalization and cultural exports.

Beyond Korea, the language is recognized as a minority language in parts of China, namely Jilin, and specifically Yanbian Prefecture, and Changbai County. It is also spoken by Sakhalin Koreans in parts of Sakhalin, the Russian island just north of Japan, and by the Koryo-saram in parts of Central Asia. The language has a few extinct relatives which—along with the Jeju language (Jejuan) of Jeju Island and Korean itself—form the compact Koreanic language family. Even so, Jejuan and Korean are not mutually intelligible. The linguistic homeland of Korean is suggested to be somewhere in contemporary Manchuria. The hierarchy of the society from which the language originates deeply influences the language, leading to a system of speech levels and honorifics indicative of the formality of any given situation.

Jeju (Jeju: 제줏말; Jeju RR: Jejunmal, or Korean: 제주어; RR: Jejueo, or 제주말; Jejumal), often called Jejueo or Jejuan in English-language scholarship, is a Koreanic language originally from Jeju Island, South Korea. It is not mutually intelligible with mainland Korean dialects. While it was historically considered a divergent Jeju dialect of the Korean language, it is increasingly referred to as a separate language in its own right. It is declining in usage and was classified by UNESCO in 2010 as critically endangered, the highest level of language endangerment possible. Revitalization efforts are ongoing.

The consonants of Jeju are similar to those of the Seoul dialect of Korean, but Jeju has a larger and more conservative vowel inventory. Jeju is a head-final, agglutinative, suffixing language, like Korean. Nouns are followed by particles that may function as case markers. Verbs inflect for tense, aspect, mood, evidentiality, relative social status, formality, and other grammatical information. Korean and Jeju differ significantly in their verbal paradigms. For instance, the continuative aspect marker of Jeju and the mood or aspect distinction of many Jeju connective suffixes are absent in Korean. Most of the Jeju lexicon is Koreanic, and the language preserves many Middle Korean features and words now lost in Standard Korean. Jeju may also have a Peninsular Japonic substratum, but this argument has been disputed.

Jeju Province (Jeju and Korean: 제주도; Hanja: 濟州道; RR: Jejudo), officially Jeju Special Self-Governing Province (Jeju: 제주특벨ᄌᆞ치도; Korean: 제주특별자치도; Hanja: 濟州特別自治道; RR: Jeju Teukbyeoljachi-do), is the southernmost province of South Korea, consisting of eight inhabited and 55 uninhabited islands, including Marado, Udo, the Chuja Archipelago, and the country's largest island, Jeju Island. The province is located in the Korea Strait, with the Korean Peninsula to the northwest, Japan to the east, and China to the west. The province has two cities: the capital Jeju City, on the northern half of the island, and Seogwipo, on the southern half of the island. The island is home to the shield volcano Hallasan, the highest point in South Korea. Jeju and Korean are the official languages of the province, and the vast majority of residents are bilingual.

Jeju Island was first settled by humans 8,000 to 10,000 years ago and the Tamna Kingdom is the earliest known civilization on the island. Beginning in the 5th century AD, the kingdom would become a tributary state of various Korean Kingdoms and briefly invaded by the Mongol Empire, before being annexed into the Goryeo in 1105 and later Joseon in 1392. Joseon ruled the island brutally and multiple uprisings occurred. Jeju Island, with the rest of mainland Korea, was annexed by the Empire of Japan in 1910. Following Japan's surrender in World War II in 1945, the islands became part of South Jeolla Province in the United States Army Military Government in Korea, before becoming a separate province on August 1, 1946. On July 1, 2006, the islands were designated a Special Self-Governing Province; it is now one of three special self-governing provinces, the others being Gangwon State and Jeonbuk State.

A lava tube, more rarely called a pyroduct, is a 'roofed conduit through which molten lava travels away from its vent'. If lava in the tube drains out, it will leave an empty cave. Lava tubes are common in low-viscosity volcanic systems. Lava tubes are important as they are able to transport molten lava much further away from the eruptive vent than lava channels. A tube-forming lava flow can emplace on longer distance due to the presence of a solid crust protecting the molten lava from atmospheric cooling. Lava tubes are often considered when preparing hazard maps or managing an eruptive crisis.

Tamna (Korean: 탐라; Hanja: 耽羅) was a kingdom based on Jeju Island from ancient times until it was absorbed by the Korean Joseon dynasty in 1404, following a long period of being a tributary state or autonomous administrative region of various Korean kingdoms.

The Go (Jeju) clan is the family name of the Lord (Korean: 성주; Hanja: 星主; RR: Seongju), that ruled West Tamna over 400 years. The Moon (Nampyeong) clan is the family name of the Prince (왕자; 王子; Wangja), that ruled East Tamna for 400 years.