Whenever we talk about war, we focus on the story’s whos and whys. Although the dates and locations were usually mentioned, they were more trivial than anything else. In reality, the physical conditions of the battlefield play a huge factor in the result of the encounters— the terrain, weather, and bodies of water, could all greatly influence how the battle would turn out.

Beyond the tanks, guns, planes, and troops that fight in a war, the terrain itself can be the enemy of both sides, with Mother Nature being a belligerent herself, inflicting casualties with rain, snow, mud, and diseases. Here are two of the worst battlefields in the history of human conflict:

Chosin Reservoir

Also known as the Battle of Lake Changjin, the critical battle took place about a month after the People’s Republic of China entered the conflict stage of the Korean War when they sent the People’s Volunteer Army to occupy the northeastern part of North Korea.

From November 27 to December 13, 1950, 30,000 United Nations Command troops led by Major General Oliver Smith fought some 120,000 Chinese troops under Song Shilun. They were attacked by surprise, which led to the Marines’ encirclement. Worse, the harsh Siberian winter reached temperatures as low as -36 degrees Fahrenheit, and both parties were exposed to the icy environment. The ground was frozen, so troops could not dig foxholes. Their weapons would often jam, fuel for tanks and planes would turn to jelly, and an incredible number of the soldiers experienced frostbite. The landscape was one of hills and mountains with sparse cover and bitterly cold winds.