The most common use of the term "natural barrier" is in geography, where it refers to a naturally occurring obstacle to movement, especially of people and especially at modest technological levels.

Mountain

Mountain

Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

s, swamp

Swamp

A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...

s, desert

Desert

A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...

s and icefields are among the clearest examples of natural barriers. River

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

s are a more ambiguous example, as they may obstruct large-scale movement across them (especially by armies) but may facilitate smaller-scale movement along them in boats, once some of the people in the region have developed the relevant technologies. Sea

Sea

A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...

s have likewise been an obstacle at first, then a convenient medium for transport

Transport

Transport or transportation is the movement of people, cattle, animals and goods from one location to another. Modes of transport include air, rail, road, water, cable, pipeline, and space. The field can be divided into infrastructure, vehicles, and operations...

 along coastlines, and finally a medium for intercontinental transport.

Natural barriers have been important factors in human history, by obstructing migration

Human migration

Human migration is physical movement by humans from one area to another, sometimes over long distances or in large groups. Historically this movement was nomadic, often causing significant conflict with the indigenous population and their displacement or cultural assimilation. Only a few nomadic...

 and invasion

Invasion

An invasion is a military offensive consisting of all, or large parts of the armed forces of one geopolitical entity aggressively entering territory controlled by another such entity, generally with the objective of either conquering, liberating or re-establishing control or authority over a...

. For example Jared Diamond

Jared Diamond

Jared Mason Diamond is an American scientist and author whose work draws from a variety of fields. He is currently Professor of Geography and Physiology at UCLA...

 argues that West European nations have been the dominant powers of the last 500 years because Europe's many natural barriers divided it into competing nation-state

Nation-state

The nation state is a state that self-identifies as deriving its political legitimacy from serving as a sovereign entity for a nation as a sovereign territorial unit. The state is a political and geopolitical entity; the nation is a cultural and/or ethnic entity...

s and this competition forced the European nations to encourage innovation and avoid technological stagnation.

Some examples of natural barriers are the Himalayas isolating Indian subcontinent from the rest of Asia, the Grand Canyon, the Dead sea, and the Mississippi river.