Atheists in the United States love to quote the Treaty of Tripoli:
As the Government of the United States of America is not, in any sense, founded on the Christian religion,—as it has in itself no character of enmity against the laws, religion, or tranquility, of Mussulmen,—and as the said States never entered into any war or act of hostility against any Mahometan nation, it is declared by the parties that no pretext arising from religious opinions shall ever produce an interruption of the harmony existing between the two countries.
This paragraph appeared in the English version of the treaty ratified by the Senate of the United States in 1797. There is an implication often made in quoting this paragraph, so I’ll squash that implication with this: the government of the United States is a separate sovereign from the the governments of each State.
When the Senate ratified the treaty, the treaty was ratified by the government of the United States. When representatives of the President signed the treaty before it was submitted to the Senate for ratification, it was signed on behalf of the presiding officer of the government of the United States.
The government of the United States is, as the treaty properly stated, not founded on Christianity. There is nothing in the Constitution that even alludes to any possibility of the government of the United States being founded or based on Christianity. But the United States is a federated republic of 50 sovereign States, each with their own government. The statement in Article 11 of the Treaty of Tripoli does not and cannot apply to the governments of each of those States, or even of just the 15 States that existed in 1797, but only to the government of the United States.
As an example to say the government of the United States is not founded on Christianity is not to also say the government of the Commonwealth of Virginia is not founded on Christianity. They are two separate sovereigns. The statement of the Treaty of Tripoli does not apply to both.
But this misrepresentation and implication is a symptom of a problem we have in the US.
People no longer really have in their minds the fact that there are 50 sovereign States that comprise the United States, or they forget the idea when it is convenient. The States were intended to be superior in all manner except the 17 enumerated powers of Article I, Section 8 of the Constitution. Again, the government of the United States is a federated republic of independent, sovereign States.
Not provinces. Not territories. States.
Even the Fourteenth Amendment cannot apply the statement of Article 11 of the Treaty of Tripoli to any other State. The only thing the Fourteenth Amendment applies to the States with regard to religion is the protections provided by the First Amendment.