I joined the Marine Corps in 1988.  Several generations of my family are Marines dating back to WWI (or the Great War).
My two brothers and I followed my dad's footsteps and joined.  In fact, we have a family photo of us in our dress blues.
I joined because I was raised a Patriot.  I have a sense of duty to my country and signed up to support and defend the Constitution of the US.  
To this day, I will still support & defend.  My oath has no expiration date!
In short, I joined because of my love of God, Country, and Corps.
oo-RAH!!! 

SlipKnoT