Where does the will to fight come from?

Have you ever been in a situation where you just didn't understand why you had to repeat the same process over and over with someone? Are somethings intrinsically present in some people and absent in others? What about the will to fight. 1% of the American population joins military service. Of that 1% there is a certain amount that truly want to be in the fight. What is it, what is that driving force within an individual that makes them have this desire? E pluribus Unum; Out of many, One. The U.S. is not a nation of native people we have many different nationalities among us. We live together and for the most part get along with each other. Other cultures look at us and sometimes say we do not have a culture of our own. There is truth in this because we are a melding of many cultures. We have a extremely strong National Identity, this national identity is what binds all of us together and makes us willing to fight as a single force not as Californians, Texans, .... but as a nation, we are Americans whether we were born here or naturalized here. We live in an environment that perpetuates the notion that we are one.

http://www.strategicstudiesinstitute.army.mil/index.cfm/articles/The-Will-To-Fight/2015/08/25