Gulf of Tonkin in the context of "Guangxi"

The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by South China, in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Philippines (mainly Luzon, Mindoro, and Palawan), and in the south by Borneo, eastern Sumatra, and the Bangka Belitung Islands, encompassing an area of around 3,500,000 km (1,400,000 sq mi). It communicates with the East China Sea via the Taiwan Strait, the Philippine Sea via the Luzon Strait, the Sulu Sea via the straits around Palawan, the Java Sea via the Karimata and Bangka Straits, and directly with the Gulf of Thailand. Additionally, the Gulf of Tonkin is part of the South China Sea.

$3.4 trillion of the world's $16 trillion maritime shipping passed through the South China Sea in 2016. Oil and natural gas reserves have been found in the area. The Western Central Pacific accounted for 14% of the world's commercial fishing in 2010.

The Red River or the Hong River (traditional Chinese: 紅河; simplified Chinese: 红河; pinyin: Hóng Hé; Vietnamese: Sông Hồng; Chữ Nôm: 瀧紅), also known as the Sông Cái (lit. "Main River"; Chữ Nôm: 瀧丐) in Vietnamese and the Yuan River (元江, Yuán Jiāng) in Chinese, is a 1,149-kilometer (714 mi)-long river that flows from Yunnan in Southwest China through northern Vietnam to the Gulf of Tonkin. According to C. Michael Hogan, the associated Red River Fault was instrumental in forming the entire South China Sea at least as early as 37 million years before present. The name red and southern position in China are associated in traditional cardinal directions. The river is relatively shallow, and carries a lot of reddish silt along its way, appearing red brown in colour.

Haiphong or Hai Phong (Vietnamese: Hải Phòng, pronounced [hǎːj fɔ̀ŋ͡m] ) is the third-largest city in Vietnam and is the principal port city of the Red River Delta. The municipality has an area of 1,526.52 km (589.39 sq mi). The city includes Bạch Long Vĩ and Cát Hải islands in the Gulf of Tonkin. It has a population of 2,130,898 in 2023. The city's economy has strength in manufacturing, as evidenced by large industrial parks and numerous smaller traditional handicraft villages. Historically, Haiphong was the first place in Vietnam and Mainland Southeast Asia to get electricity.

In the imperial era of Đại Việt, the Bạch Đằng River in Haiphong was a place of many legendary victories, led by now-legendary commanders Ngô Quyền and Trần Hưng Đạo. In the 16th century, Mạc dynasty promoted the coastal settlement as a secondary capital, growing to become an important port town of Đàng Ngoài. After the French conquest of Vietnam, in 1888, the president of the French Third Republic, Sadi Carnot, promulgated a decree to establish Haiphong as one of the principal cities of French Indochina. From 1954 to 1975, Haiphong served as the most important maritime city of North Vietnam. It was one of the directly controlled municipalities of a reunified Vietnam with Hanoi and Ho Chi Minh City in 1976.

The China–Vietnam border is the international boundary between China and Vietnam, consisting of a 1,297 km (806 mi) terrestrial border stretching from the tripoint with Laos in the west to the Gulf of Tonkin coast in the east, and a maritime border in the Gulf of Tonkin and South China Sea.

While disputes over the terrestrial border have been settled with the signing of a land boundary treaty between the two countries, the maritime border is currently undefined due to disputes over the ownership of territorial waters and islands, including the Spratly and Paracel Islands.

In international law, national boundary delimitation (also known as national delimitation and boundary delimitation) is the process of legally establishing the outer limits ("borders") of a state within which full territorial or functional sovereignty is exercised. National delimitation involves negotiations surrounding the modification of a state's borders and often takes place as part of the negotiations seeking to end a conflict over resource control, popular loyalties, or political interests.

Occasionally this is used when referring to the maritime boundaries, in which case it is called maritime delimitation.The term "maritime delimitation" is a form of national delimitation that can be applied to the disputes between nations over maritime claims. An example is found at Maritime Boundary Delimitation in the Gulf of Tonkin. In international politics, the Division for Ocean Affairs and the Law of the Sea (Office of Legal Affairs, United Nations Secretariat) is responsible for the collection of all claims to territorial waters.

Đại Việt (大越, IPA: [ɗâjˀ vìət]; literally Great Việt) was a Vietnamese monarchy in eastern Mainland Southeast Asia from the 10th century AD to the early 19th century, centered around the region of present-day Hanoi. Its early name, Đại Cồ Việt, was established in 968 by the ruler Đinh Bộ Lĩnh after he ended the Anarchy of the 12 Warlords, until the beginning of the reign of Lý Thánh Tông (r. 1054–1072), the third emperor of the Lý dynasty. Đại Việt lasted until the reign of Gia Long (r. 1802–1820), the first emperor of the Nguyễn dynasty, when the name was changed to Việt Nam in 1804. Under rule of bilateral diplomacy with Imperial China, it was known as Principality of Giao Chỉ (chữ Hán: 交趾) (975–1164) and later Kingdom of Annam (chữ Hán: 安南) (1164–1804) when Emperor Xiaozong of Song recognized Đại Việt's independence and upgraded its status from principality to kingdom.

Đại Việt's history was divided into the rule of eight dynasties: Đinh (968–980), Early Lê (980–1009), Lý (1009–1226), Trần (1226–1400), Hồ (1400–1407), and Later Lê (1428–1789); the Mạc dynasty (1527–1677); and the short-lived Tây Sơn dynasty (1778–1802). It was briefly interrupted by the Hồ dynasty (1400–1407), which changed the country's name to Đại Ngu, and the Fourth Era of Northern Domination (1407–1427), when the region was administered as Jiaozhi by the Ming dynasty. Đại Việt's history can also be divided into two periods: the unified state, which lasted from the 960s to 1533, and the fragmented state, from 1533 to 1802, when there were more than one dynasty and several noble clans simultaneously ruling from their own domains. From the 13th to the 18th century, Đại Việt's borders expanded to encompass territory that resembled modern-day Vietnam, which lies along the South China Sea from the Gulf of Tonkin to the Gulf of Thailand.

Bạch Long Vĩ island is located in the Gulf of Tonkin, about halfway between Haiphong (Vietnam) and Hainan Island (China). The island is an offshore district of Haiphong city. Fishing comprises the majority of economic activity in the Gulf of Tonkin, and Bạch Long Vĩ is a major nursery and harvesting area for fish eggs. More than 50 species of commercial fish are abundant in the area (ADB 1999).

Cát Hải [kaːt˧˥:ha̰ːj˧˩˧] is an archipelago in the Gulf of Tonkin. Its full name is Cát Hải Special Zone of Hải Phòng City belonging to Hải Phòng city in the Red River Delta of Vietnam.