WW1- Exhaustion

Historical- Exhaustion was a real problem in WW1, and the war to follow it, WW2. People would just fall down and die in the middle of nowhere because they couldn't take it anymore. 

Literary- In Owen's "Dulce et Decorum Est" he talks about being knock-kneed and coughing like hags. This just perfectly describes the way the soldiers at the time were doing.