Christian nationalism is the school of thought that the Bible and Christian tradition (like the Church Fathers) can and should influence a nation's legislation. It is thus closer to traditional Catholic teaching than "separation of Church and State" and its related errors. Project 2025, which JD Vance supports, is a Christian nationalist platform: "The project also seeks to infuse the government and society with conservative Christian values.[11][12] Critics have characterized Project 2025 as an authoritarian, Christian nationalist plan to steer the U.S. toward autocracy.[11][13][14][15] Legal experts have said it would undermine the rule of law,[16] separation of powers,[5] separation of church and state,[17] and civil liberties.[5][16][18]" https://en.wikipedia.org/wiki/Project_2025

Below is an example of Christian nationalism in Zambia:

"We the people,” begins the Zambian constitution’s preamble. It sounds familiar to Americans, but a few words later is a phrase that American Christians haven’t ever heard: “declare the Republic a Christian nation while upholding the right of every person to enjoy that person’s freedom of conscience or religion.”
It’s not just lip service. Zambia’s laws draw on Christian tradition to ban, for example, both ɧoɱosɛҳųαƖ behavior and pornography. Earlier this year, a Zambian judge sentenced a German tourist to six years in jail with hard labor—for oral sex. “Customs of other countries, which are an abomination here, must not be allowed to be practiced by tourists or anybody,” the judge said.
It’s not just a political thing, either. More than 80 percent of the country’s 9 million residents are professing Christians—and the numbers are growing. By 2025, predicts The World Christian Encyclopedia, 87.8 percent of the country will be Christian. By 2050, it should top 92 percent."

https://www.christianitytoday.com/2002/02/one-african-nation-under-god/