That is the point. People are getting killed regardless. Some of them are killed in the name of god, others are, in the name of capitalism, others are in the name of nations.
When a person is killed, it is killed in the name of the belief that the killer of that person holds at the moment of the murder.
If a Christian kills a Muslim because he is a heretic, then the kill is to be under religion. If the Muslim simply is fighting for Iraq and not the US, then the kill is to be considered under the US. If they are just having unspeakable relationships with a woman and they kill each other because one cheated, then the kill should absolutely not be credited under god or nation.