Natural border in the context of "Transylvania"

The Chilia branch (Romanian: Brațul Chilia; Ukrainian: Кілійське гирло, romanized: Kiliiske hyrlo) is one of three main distributary channels of the river Danube that contribute to forming the Danube Delta. Lying at the northernmost area of the delta, the distributary creates a natural border between Romania and Ukraine (see Romania-Ukraine border) and is named after the two towns carrying the same name, located across from one another on both banks: Kiliia, on the northern, Ukrainian bank and Chilia Veche (Old Chilia) on the southern, Romanian bank.

The other two main branches of the Danube are the Sulina branch and the Sfântu Gheorghe branch.

The Tatra Mountains (pronounced), Tatras (Tatry either in Slovak (pronounced [ˈtatri] ) or in Polish (pronounced [ˈtatrɨ]) - plurale tantum), are a series of mountains within the Western Carpathians that form a natural border between Slovakia and Poland. They are the highest mountains in the Carpathians. The Tatras are distinct from the Low Tatras (Slovak: Nízke Tatry), a separate Slovak mountain range further south.

The Tatra Mountains occupy an area of 785 square kilometres (303 sq mi), of which about 610 square kilometres (236 sq mi) (77.7%) lie within Slovakia and about 175 square kilometres (68 sq mi) (22.3%) within Poland. The highest peak, called Gerlachovský štít, at 2,655 metres (8,711 feet), is located north of Poprad, entirely in Slovakia. The highest point in Poland, Rysy, at 2,500 metres (8,200 ft), is located southeast of Zakopane, on the border with Slovakia.

Mountain warfare or alpine warfare is warfare in mountains or similarly rough terrain. The term encompasses military operations affected by the terrain, hazards, and factors of combat and movement through rough terrain, as well as the strategies and tactics used by military forces in these situations and environments.

Mountain ranges are of strategic importance since they often act as a natural border and may also be the origin of a water source such as the Golan Heights. Attacking a prepared enemy position in mountain terrain generally requires a greater ratio of attacking soldiers to defending soldiers than a war conducted on level ground. Mountains present natural hazards such as lightning, strong gusts of wind, rockfalls, avalanches, snowpacks, ice, extreme cold, and glaciers with their crevasses; in these ways, it can be similar to cold-weather warfare. The generally uneven terrain and the slow pace of troop and material movements are additional threats to combatants. Movement, reinforcements, and medical evacuation up and down steep slopes and areas in which even pack animals cannot reach involves an enormous exertion of energy.

The Amur River (Russian: река Амур) or Heilong River (simplified Chinese: 黑龙江; traditional Chinese: 黑龍江) is a perennial river in Northeast Asia, forming the natural border between the Russian Far East and Northeast China (historically the Outer and Inner Manchuria). The Amur proper is 2,824 km (1,755 mi) long, and has a drainage basin of 1,855,000 km (716,000 sq mi). If including its main stem tributary, the Argun, the Amur is 4,444 km (2,761 mi) long, making it the world's tenth longest river.

The Amur is an important river for the aquatic fauna of Northeast Asia. The river basin is home to a variety of large predatory fish such as northern snakehead, Amur pike, taimen, Amur catfish, predatory carp and yellowcheek, as well as several species of trout and anadromous salmonids. The largest fish species in the Amur is the kaluga, a sturgeon that is one of the largest freshwater fish in the world, attaining a length as great as 5.6 m (18 ft). The Amur is also home to the northernmost populations of the Amur softshell turtle and Indian lotus.

Kinshasa (/kɪnˈʃɑːsə/; French: [kinʃasa]; Lingala: Kinsásá), formerly named Léopoldville from 1881–1966 (Dutch: Leopoldstad), is the capital and largest city of the Democratic Republic of the Congo. Kinshasa is one of the world's fastest-growing megacities, with an estimated population of 17.8 million in 2024. It is the most densely populated city in the DRC, the third-most populous city and third-largest metropolitan area in Africa, and the world's twenty-second most populous city and fourth-most populous capital city. It is the leading economic, political, and cultural center of the DRC, housing several industries including manufacturing, telecommunications, banking, and entertainment. The city also hosts some of the DRC's significant institutional buildings, such as the People's Palace, Palace of the Nation, Court of Cassation, Constitutional Court, African Union City, Marble Palace, Martyrs Stadium, Government House, Kinshasa Financial Center, and other national departments and agencies.

The Kinshasa site has been inhabited by Teke and Humbu people for centuries and was known as Nshasa before transforming into a commercial hub during the 19th and 20th centuries. The city was named Léopoldville by Henry Morton Stanley in honor of Leopold II of Belgium. The name was changed to Kinshasa in 1966 during Mobutu Sese Seko's Zairianisation campaign as a tribute to Nshasa village. Covering 9,965 square kilometers, Kinshasa stretches along the southern shores of the Pool Malebo on the Congo River. It forms an expansive crescent across flat, low-lying terrain at an average altitude of about 300 meters. Kinshasa borders the Mai-Ndombe Province, Kwilu Province, and Kwango Province to the east; the Congo River delineates its western and northern perimeters, constituting a natural border with the Republic of the Congo; to the south lies the Kongo Central Province. Across the river sits Brazzaville, the smaller capital of the neighboring Republic of the Congo, forming the world's closest pair of capital cities despite being separated by a four-kilometer-wide unbridged span of the Congo River.