Conventional armed forces like the United States use mechanized or 'High Tech' warfare. This type of force is at it's greatest advantage:
1) Over water. It requires warships to contest the surface, aircraft and missiles to control the air above, and submarines to protect and contest beneath the surface.
2) Desert. Since the invention of the internal combustion engine, the desert has been the 2nd best place to deploy mechanized forces. It is called a quartermasters nightmare and a tacticians dream. It requires mechanization to support any forces deployed. The desert gives thermal imaging and other 'high tech' equipment one of the most ideal environments on the planet.
3) Open land. The stepps in Russia are a good example. The only natural obstacles are rivers.
Mechanized forces are at the greatest disadvantage in:
1) Mountains. Aircraft are limited in ability to maneuver. Low-tech men and weapons are more easy to hide, deploy and move. High tech weapons are far less effective, armor is less mobile and the uneven ground make line of sight difficult.
2) Swamps. Swamps are only marginally more desirable for mechanized forces to fight in. Aircraft can maneuver better than in mountains.
3) Cities and forests. Line of sight is difficult to establish along with the certainty of hitting non-armed people in cities.
I have been hearing some people say that the United States should withdraw from Iraq and re-depoly some (Not all) of the withdrawn forces into Afghanistan. Moving a 'High tech' force like the U.S. military from a desert environment into the mountains of Afghanistan would shift the fight from one of the most ideal environments on the planet Earth into the least ideal environment.