The American government is, theoretically, founded on the principle of separation of church and state. As commonly understood, it means that there is no state-mandated or supported religion, nor a prohibited religion. People are free to believe in whichever religion they choose, or no religion at all, as long as the practice of that religion does not violate any laws. It is also understood that government shall not be dictated to or controlled by an established religion. Other than that, there is a lot of murkiness in the relationship between government and religion.
When one considers the influences of religious concepts on daily life, we see that it is virtually impossible to separate church and state. Whether one is a devoted practitioner or an atheist, he must realize how closely government and religion have been intertwined throughout history into the present era, for better or worse. Let us trace this relationship through a quick sketch - somewhat imaginative - of mankind's history, which may not be too far from actual developments. (I would welcome essential corrections to my simple narrative by knowledgeable historians.)
Primitive human societies of extended families (tribes or clans) resembled small herds of wild animals with a dominant male. Mankind, distinguished by a capacity to use tools to provide food, clothing, and shelter, and to acquire language, gradually expanded its ability for learning. For people of those times, life experiences were based upon the phenomena of nature, which were both benign and brutal. In lieu of knowledge acquired by experience and science, there were many more questions than answers.
In the void of ignorance, people invented stories to explain the unknown. Thus deities were invented who manipulated events behind the scenes -- like the deus ex machina of later Greek drama. The origin of the world was attributed to these deities, and myths were invented to explain the operations of the world. This led to the origin of a class of priests who introduced rituals of sacrifice and offerings to placate these gods. The "learning" of these priests qualified them as wise men who could act as intermediaries to the gods, make decisions and settle disputes among the people, thus becoming the original governing authority and the foundation of systems of justice. As societies evolved and knowledge of the world increased, new religions arose to expand upon the primitive myths, oftentimes based on dreams of spiritually inspired people.
But there was another element to the evolution of government. Along with or preceding the priest class, there was also the warrior -- originally the dominant male. Warfare was an integral part of early history. During the hunting and foraging era of mankind, tribes followed migratory animal herds and would come in contact with other tribes. Territorial conflicts ensued, which necessitated developing battle skills derived from hunting skills. The best and bravest warriors would be honored and assume positions of tribal leadership.
Our imaginative narrative continues into historical periods when tribes settled down in agricultural-based villages and, eventually, city-states. The warrior chief, now king, perhaps combined powers of both the general and the priest. In some instances, the aura of power endowed him as a favorite of the deities in the eyes of the people or priests, elevating him to the status of a demigod. (It would be interesting to know if the kings actually believed all this or just played along to enhance their powers). The "divine" attribute of the king was endowed upon his heirs to perpetuate the succession of power. These are the themes we see in "god-kings" of the Egyptian civilization, for example, with some elements persisting into the second millennium, when kings possessed "divine rights"; or when church and state were combined in the Holy Roman Empire.
The modern state -- where it exists -- has evolved from both the religious and the military. From primitive rituals, religion blossomed into codes of ethics and behavior eventually implanted in texts held to be sacred. Over time, modified by contemporary ethics, they filtered down into secular laws that, in principle, constitute the basis of modern governments. The transition from the religious to the secular began in the time of the ancient Greeks. The Greeks and Romans had their deities but, as wealth and leisure were acquired, a culture of arts, commerce, science and philosophy arose from which sprang the roots of popular or democratic government -- a government composed of or influenced by members of society other than strictly from the priest or military class.
With the downfall of the Greek and Roman worlds, a new wave of Christian/Islamic militarism swept the Medieval World through the time of the Crusades. This was followed throughout Europe by the military/religious conflicts during the Reformation with the birth of new Protestant sects and of divisions within Islam. The Reformation was primarily a revolt ignited by the changing world of the Renaissance against a central religious establishment of unscientific traditions and decadent authority. During the era of exploration and colonization, catholicism was introduced to the New World by conquest. Throughout most of history, a person's religion was a significant part of his identity that was imposed upon him by the ruling authority as well as by cultural and family traditions. There have always been non-conformists, but it was only until the recent modern age that individual choice of religions and non-belief became commonplace.
We see today in the Arab world and elsewhere an anarchy of religious and political turmoil of medieval proportions that should have no place in the modern world. Has there been no real progress in civilization with respect to religious and philosophical ideals of universal love and the preciousness of all creation? Many present day religious cults are at a stalemate of meaningless rituals and ceremony, created to perpetuate a priestly or governing authority, that overrides any humanistic aspirations for world peace and harmony. Must we have wars, oppression and impoverishment forever?
Does the promise of a better world lie in the victory of one religion over another or the conversion of non-believers; or, rather, in a new universal religion of goodwill founded on the highest moral principles of our humanistic heritage? I can see no real progress in civilization - smarter phones and TVs and self-driving cars, etc. aside - until people are freed from the prison of religious and political thought control, and given free choice of what to believe, based upon exposure to the world's most esteemed schools of thought and factual knowledge, through better education and communication.