There are basically two ways of winning a war: crushing (i.e. killing) the enemy militarily or breaking his will to fight to so that he gives up and goes home. Sometimes the two go hand in hand: military defeats tend to demoralize troops and make them less willing to continue fighting and face more defeat and risk of death. But in order for the enemy to give up the fight, they must believe that surrender is better than fighting. If they believe that they will be tortured or executed if captured, even demoralized men will fight to the death. Propagandists on both sides understood this simple equation, and worked hard to convince the other side that that they should give up.
Here is an interesting propaganda leaflet dropped by the allies from airplanes over Bulgarian forces during World War 1. The leaflet consists of an idyllic picture of Bulgarian prisoners of war enjoying warm food and easy circumstances at the hands of their allied captors, and there is also a letter describing how the allies treat their Bulgarian prisoners. The idea was to convince the Bulgarians to give up and escape the horrors of war for the relative comfort of a prisoner of war camp run by the humane Brits and French.
In fact the allied powers were not known for their gentle treatment of POWs. The Russians transported their Austrian and German POWs to Siberian prison camps where many died from disease and malnutrition, brought on by shortages affecting the disintegrating Russian Empire, which made feeding prisoners of war difficult and certainly not a high priority. The French and Germans used prisoners of war for forced labour, even using them to work in active military zones where they faced death at the hand of “friendly” fire from their former comrades.