Firstly no one disputes that the thirteen colonies were founded by Christians and that many of these colonies had explicitly Christian laws.
You can stop right there and you'd be correct.
Hence the Salem Witch Trials under the Puritan theocracy. Under Massachusetts Puritan Law your religion was dictated to you, if you were not a member of the Puritan Church you were not considered a freeman or permitted to vote. Even Quakers could not hold office.
One law forbade the wearing of lace, another of "slashed cloaths other than one slash in each sleeve and another in the back." The length and width of a lady's sleeve was solemnly decided by law. It was a penal offense for a man to wear long hair, or to smoke in the street, or for a youth to court a maid without the consent of her parents. A man was not permitted to kiss his wife in public. Captain Kimble, returning from a three-years' ocean voyage, kissed his wife on his own doorstep and spent two hours in the stocks for his "lewed and unseemly behavior."
Slavery was ensconced in law, Christmas outlawed, blasphemers and those who persisted in the wrong faith executed.
So - yes, the colonies were indeed founded on Christian principles.
Those atrocities were likely carried out by believers and NOT Christians. It's easy to point out the bad things that "Christians" have done in the name of their "faith". It would be just as easy to do the opposite. Or to point out the atrocities done by atheists is the past. You can make the "stats" look as good or as bad as you want to do. It doesn't change your first statement in your reply.
The COLONIES were founded upon religeous principles which were heavily Christianity in nature.
It was so bloody awful that when it was time to write a constitution there was a strong argument - with support from religious leaders - to maintain a separation of Church and State. They argued this as a Christian principle - referring to Matt 22:21 and other verses.
The constitution doesn't refer to seperation of church and state as you INFER. SEPERATION OF CHURCH AND STATE IS SIMPLY A POLITICAL DOCTRINE AND IS NOT FOUND IN THE CONSTITUTION. The 1st amendment does say that the state will not interfere with religeous exercise and worship. What is so hard to understand about that? The 1st amendment also disallows the government to prohibit free exercise of religion.
So exactly when the US was founded is rather irrelevant.
That went to left field.
When it adopted its constitution that constitution was and is explicitly secular, making 'that which is Caesars' clearly separate from the things that are God's. It explicity did not establish the US as a Christian nation.
You are explicittly wrong. A document can NOT be considered secular when there are PROVISIONS allowing for and defending the free exercise of religion.