For food principally. It may be a sad fact, but animals often have to do that to survive. Watch wildlife films on Africa some time.
If lions do not kill wildebeest, zebras or antelopes, what do they eat? Turning lions into vegans is not going to happen and then you end up with no lions. Humans do have the choice to become vegetarians or vegans though.
That is down to the conscience (and possibly circumstances, particularly in the third World) of the individual concerned.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.