What are the major causes of infertility in couples?

Why is it that many couples nowadays are unable to concieve?

stress, polution, unsuitablility, bad diets, rubbish technique, bad relationship, dodgey water additives, too much alcohol, drug dependency, inherited disorders, leaving it too late.

Chemicals in out diet from processed food, not enought exercise, smoking, disease.
Man - low or inactive sperm
Woman - not producing eggs, damaged womb, blocked fallopian tubes
First of all too much tension or thoughts about tension leading to tension.
Too tight under garments especially by gents leading to over heating of the private parts.
Genes, smoking, drinking, STD's in younger years, previous abortion. There are many reasons, but the one's I've listed are the most common.
http://www.mcfivf.com/infertility_causes...
I think alot of it is stress. People work to damn hard these days, and they have way too much stuff going on. And also I think diet is to blame. People eat too much processed food and drink too much alcohol.