The muscles in your legs account for a large percentage of your total muscle mass. When you engage those muscles in walking for an extended period you also force your heart, lungs and other organs to increase their activity. When your body detects the demands, it accommodates and becomes more efficient.
That efficiency is called "physical fitness.
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.