First of all, I think it's important to look at the overall Biblical narrative of the concept of nations and peoples and countries. The Bible defines a nation as a "family", if you look at the way "family" and "nation" is referenced across the Bible.

At the very start of the Bible, in the Old Testament, it is clear that God wants human beings to live separated in their own countries and nations. One of God's first commandments after Noah leaves the ark is that they should "be fruitful and multiply and replenish the earth" (Genesis 9:1) -- the exact same commandment he gave to Adam and Eve in Genesis 1:28.

At the tower of Babel in Genesis 11, humanity has come together to build an enormous temple that will reach in to heaven. As a result. God confuses their languages and once again spreads them out across the earth as he originally intended. What's important to keep in mind is that nations and peoples already existed before the tower of Babel. God gave us our peoples and nations and countries. This is even spelled out explicitly in Acts 17:24-26, where it says: "God that made the world and all things therein [...] And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation."

When God gave his promise to Abraham, He explicitly tells us that the point of His promise is that "through thee [Abraham] shall ALL of the NATIONS of the earth be blessed." The fact that he uses the plural, "nations", is important, because this is a key to realizing that God intends for all of the nations that HE CREATED to remain until the very end. because in the Book of Revelation, the different "NATIONS" are mentioned over and over again. In Matthew 25:32, it says that "before him shall be gathered ALL NATIONS: and he shall separate them one from another, as a shepherd divideth his sheep from the goats." It is clear that the nations remain until Christ returns to this earth.

Now, let's get in to some specific Biblical mentions of God forbidding race mixing and nation mixing. In Leviticus 21:14-15, God says to Moses: "A widow, or a divorced woman, or profane, or an harlot, these shall he not take: but he shall take a virgin OF HIS OWN PEOPLE to wife. Neither shall he profane his seed among his people: for I the Lord do sanctify him."

This entire passage is testament to the fact that God intends for men to marry within our own nations and not to "profane his seed among his people". People will typically use two arguments to try to debunk this doctrine:

1)They'll tell you that Leviticus isn't applicable to Christians because it dealt specifically with the priesthood of the Israelites, and not with the common man. There are two problems with that argument. A) if God's "higher standard" for the priesthood is that they marry within their own nation, then it's clear that God's ideal marriage is not a race mixed marriage. What's good for the goose is good for the gander. And B) we as Christians are ALL PRIESTS. The idea of the "priesthood of the believer" is one of the main beliefs of Bible believing Christianity. Every single Christian is a priest, and there is no difference between the priesthood and the congregation. When Christ died on the cross, the cloth that separated priests for church-goers was torn. So this passage 100% applies to all Christians. as does all of Leviticus.

2)They’ll say God was only referring to other believers, not specifically your own seed, just other believers. It is true that God commands us to only marry other believers, but that is a completely different commandment that's brought up on many other occasions as a separate argument. When Leviticus 21:14 is specifically applied by the Israelites within the Bible itself, it is clear that the passage is referring specifically to marrying within your own people, and not just other believers. In Ezekiel 44:22. Ezekiel specifically brings up this commandment, and it is quoted like this:

"Neither shall they take for their wives a widow, nor her that is put away: but they shall take maidens OF THE SEED of the house of Israel, or a widow that had a priest before."

So, it is clear that the Bible is referring to your genetic seed, namely your own people, your own nation -- not other believers. Believe it or not, but Leviticus 21:14 is actually applied on a 2nd occasion within the Old Testament. In 2 Chronicles 22, we learn that the Israelites took this commandment very strictly, because Jehoshabeath was not even allowed to marry within the broader house of Israel, but she was required to specifically marry within her own tribe of Judah. When it comes to only marrying other believers: yes, the Bible is extremely clear that we should not marry non-believers.

This is clear both from the Old Testament and from the New Testament. But that is a completely separate argument. And I interpret these Old Testament passages (Leviticus 21:14, Ezekiel 44:22, 2 Chronicles 22, etc.) literally: TAKE A WOMAN OF YOUR OWN PEOPLE FOR WIFE. These passages NEVER mention the idea that she only needs to be a believer. It's nonsensical to pretend that it's solely referring to believers in God when none of the passages mention that at all.

Some Christians have a warped idea that because we are Christians, we belong to one gigantic globalist nation, and that our old physical nations don't matter. This is clearly completely false, because

1)God intended the "NATIONS" to be saved, not one gigantic nation.

2) This is mentioned nowhere in the entire Bible, in fact, nations and peoples and tongues and kindreds are continuously mentioned throughout the entire Bible from Genesis to Revelation.

It is true that we as Christians together spiritually form the "body of Christ" and that we are a "special people, a royal priesthood, a chosen generation" before Christ, but as human beings living on this earth, we belong to nations and peoples and kindreds that God intended us to belong to and that God created.  God NEVER intended all of humanity to be mixed. In fact, it is clear from Revelation that when Satan comes in the end-times, he will be the one to unite all of humanity under a one-world globalist government and a one-world religion where everyone will live in peace and believe in Satan.

The Bible says that Jesus Christ came not to bring peace or to unite, but to divide. The Bible is strictly against globalism. If it was true that God or Jesus intended us to all live together as one gigantic nation, then why did the Holy Ghost speak in different languages to all of the adherents at the day of Pentecost? Why does Jesus Christ give specific messages to specific churches in specific nations in Revelation? Why did God divide us up on numerous occasions in the Old Testament? Why was God's promise that all NATIONS should be blessed? Why are the nations still in existence when Christ returns?!

It's a completely false, Satanic narrative that nation mixing, race mixing, globalism, mass immigration and nation-wrecking is Biblical. That is false. It is in Satan’s name.