People forget that nations like the USA, China, Russia, and Iran are just Gentile nations, some of which are blessed because of their favor towards the gospel. However, the only nation with a specific national covenant is Israel. We can’t apply scriptures that are specific to Israel or the Kingdom of God (which are monarchies) to a democratic republic nation like the USA. Unfortunately, people love cherry-picking bible verses out of context to make human agenda-based arguments. From a biblical perspective, American nationalism is no different from Chinese, Russian, or Iranian nationalism. There are Hindu Nationalists in India, and Buddhist nationalists in places like Cambodia, Laos, and Myanmar that persecute people of Abrahamic faiths.
Nationalism itself is just political hatred of anyone that is with a certain group. In fact, the word Nazi is a portmanteau of the German phrase “Nationalsozialistische Deutsche Arbeiterpartei” which in English is National Socialist German Workers. Nationalism has no place in the Kingdom of heaven since God wants all nations to be gathered under the new covenant. The Great commission according to Matthew 28:18-20 is to teach all nations. The word nation in the new testament is translated from the Greek word ethnos (ἔθνος) which is where we get the English word ethnicity. This means that biblical nations aren’t specifically referring to nation-states but rather people groups (ethnicities). This goes back to the ethnic separation by language at the Tower of Babel in Genesis 10 and 11.
Believers are ambassadors for Christ (2 Cor 5:20), which means we represent Christ’s kingdom on the earth. This is because believers are in the world but not of it world (John 17:14-15), and we are actually citizens of heaven (Phil 3:20-21). A believer’s nationalist allegiance is to the kingdom of God, not to any nation on earth. The only possible exception would be an Israelite and that is only when the Messiah himself comes to rule that nation.