Emmanuel,
In the end they are protecting each other, their fellow Soldiers, Marines, Sailors and Air Force, the majority of which are American citizens but to them they are all brothers (and a few sisters too). They do so while in service to our country so I think you can say they are protecting our country because "protecting " Americans is serving our country. May sound silly but in the end they are thinking of themselves and their buddies when the rubber hits the road.   
They fight for each other and fight because that is their job.. ... what our country asked (ordered) them to do. 
My husband said in Vietnam they were fighting for their lives and their brother soldiers lives, for each other so they could come home.
Yes, I stayed up all night to figure out something to say........I paid my subscription.......