I think you're getting "nation" and "nation-STATE" mixed up.
Nation - Group of people with shared features.
State - Group with a monopoly on violence in a particular territory.
Nation-State - Group of people with shared features who possess a monopoly on violence in a particular territory.
The way I see it, there is nothing wrong with nations per se, granted they are voluntary. Rothbard wrote about this. https://mises.org/journal-libertarian-studies/nations-consent
The issue that arises is when a nation forces itself onto others.
The Bible supports the freedom of association necessary for a Christian nation to exist in a couple of verses:
"Therefore, whatever you want men to do to you, do also to them, for this is the Law and the Prophets." Matthew 7:12 NKJV
"But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you," Matthew 5:44 NKJV
