The effect of world war i on the evolution of psychological testing was to

Soldiers not only suffered on the battlefield. Veterans often needed long-term care owing to the physical and psychological impact of war. The close proximity of people in wartime conditions meant diseases such as tuberculosis could easily spread. The exertion of battle could highlight other health problems including asthma and heart conditions. Some conditions such as trench foot, an infection of the feet caused by cold, wet and unsanitary conditions, were very specific to the water-filled trenches of the First World War.

Democracy and darwinism would be my answer.