Civil Strife! Conflict broke out during your youth causing social upheaval, your family was involved in the conflict (Work with your DM to detirmine your families involvement)
Divorce: During your adolescence your parents split up and you were forced to chose which parent to live with (Work with your DM to detirmine the details)
When you become an adult you learn to used a weapon (of your choice) appropriate for your culture and social standing. (work with your DM to determine details)