“As humans became more numerous and the populations increased in desirable areas, a code of conduct was needed to prevent constant bloodshed. A structure which could define families and social mores”

>>A human society, and an implicit social contract, in other words.

“A definition of marriage, the defense of personal property, the occasions when murder or maiming was and was not appropriate. “

>>A civil authority (i.e., government.

“All the rules which are needed by todays societies including a power structure and a police force to enforce those rules.”

>>A legal system.

“Many of these "laws" were and still are based on religious beliefs.”

>>here’s where I believe you’ve got it backwards—societies incorporated existing codes of conduct into the religious traditions they authored, not the other way around.

“If religion is eradicated civilization will lapse back into the barbarism it came from.”

>>Why? Assume religion was eradicated tomorrow—what reason would we have, as a society, to abandon the rule of law we’ve observed for centuries?