Background
Geography shapes history because it is where all history takes place.  Geography is the study of people, their environment, and their resources.  Civilizations are influenced by access to various types of resources, by geographical features that either protect, or isolate, and by the area in which they live.  Some of these geographical resources and features are, rivers, mountains, oceans, irregular and regular coast lines, and islands.

Geographical Features
Rivers	Rivers provide fresh water for irrigation, act as trade routes & invasion routes, and provide fertile soil along their valleys.  Major river valleys such as the Nile, Tigris-Euphrates, Indus, and Yellow, all were home to early civilizations.
Mountains	Mountains often act as barriers for civilizations.  This can have a positive effect in that it protects a culture from invasion.  An example of mountains as a barrier would be the Himalayas protecting early India from China.  They can also have a negative effect by preventing cultural diffusion.  An example of this would be the near isolation of the Incan Empire along the Andes.
Oceans	Oceans often act as barriers for civilizations, but can also be a source of food and livelihood. The barrier effect has both positive and negative aspects. A positive example would be the Pacific Ocean was a barrier to Korean invasion of Feudal Japan.  A negative example would be the Atlantic Ocean prevented cultural diffusion between Mesoamerica and the rest of the world for centuries.
Irregular Coastline	An irregular coastline has many natural harbors.  This feature has both positive and negative effects.  An example of a positive effect would be the British Islands which have many natural harbors.  This feature allowed them to develop a strong Navy, and trade and culturally diffuse with the world.  A negative example would be North & South America, which also has many natural harbors.  This provided easy access for the Europeans when the began to explore, and eventually conquer the continents.
Regular Coastline	Regular coastlines have few to no natural harbors.  This is a barrier effect with both positive and negative consequences.  Africa has a regular coastline.  A positive effect of this was that it was difficult to invade Africa by sea.  A negative effect was that Sub-Saharan Africa remained isolated from the rest of the world for many centuries.
Islands	Islands often act as barriers to both invasion and cultural diffusion.  Japan has been able to stay free of foreign control though most of its history, but has also been isolated from the world for centuries at a time.  Great Britain was able to stay free of German control during World War II because they are an island nation.
Rainforests	Rainforests often act as barriers, but can also be a resource center.  As a barrier, they prevent invasion and cultural diffusion.  An example would be the African rainforests.  They can also be a source of raw materials. An example would be the Amazon Rainforests which provide hardwoods, medicines, and other raw materials to many countries in South America.
Deserts	Deserts often act as barriers.  An example would be the Sahara Desert that protected lower Africa from invasion for many centuries.  But, the Sahara also prevented cultural diffusion to this area.