The reason behind this cannot be far fetched:
1.Giving out girls at a very young age.
I read on Saturday punch today that a 21 year old girl who has been married for 11 YEARS files for divorce because shes not in love with her husband after four children.I wonder why some ppl back up their selfish interest with Quran.The Quran never says you should do things without your brain.What happen when you give out your 8yrs old daughter to your sixty yrs old friend?What happens if the man dies few years after?What happen if she grew up and realise shes not in love with her husband?.Food for thought.
2.Fighting religious war.
This is another reason why many young northern men loose their lives.Just like d case of boko haram.Only God knows how many young men were dead in this so calld religious war,it cant be less than 20000 .A muslim friend keep agueing that Shekau is not a true muslim.If he is right,why cant the true muslim rise up against him and defend the true cause of islam.

These ar some of d reasons that reduce the population of northern men.The situation is not as worse as this in other parts of the country.They cause their own problem theirselves.If care is not taken thesituation will become worse and northern Nigeria will not remain the same again.