If the P trap dries out, the sewer flies will get into the premises. Try to remember to pour a gallon of water into seldom used drains so the trap is full of water. This is most important if you have floor drain showers that you don't use, I know from experience.
They will also come up basement floor drains, check ball inserts are available to alleviate that issue if you now they are coming up a basement floor drain that can't be plugged. They usually come from the garbage disposal, filling the disposal with enough to plug it and then pouring in a load of bleach will kill off the fly eggs growing in the disposal drain.
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.