But not for long. In 391 A.D., Emperor Theodosius made Christianity the state church, and the persecution of other religions started in full force. Christians, who were once the persecuted, became the persecutors. For thousands of years church and state were intermingled - and Christianity often warred among itself. Religiously inspired insurrections, oppressions, and purges were the dominant reality.
Then something remarkable happened. America's independence allowed a new thinking to take hold. Led by Thomas Jefferson and James Madison, Virginia protected the free exercise of religion by eliminating its state support of an established religion. Soon, with Madison's prodding, the federal government (and most states quickly fell in line) embedded in the First Amendment the protection of religious worship and the prohibition of a government church.
Unfortunately, that lesson is still not yet learned across the globe. Iran, as just one example, is a theocracy of the most brutal order.
When you attend your next religious service (or choose not to do so), remember that the legacy of the Edict of Milan was short-lived, and so may be the First Amendment. History ebbs and flows - just because we have the freedom today does not mean it shall always be so. Work to preserve your liberty everyday.