This sort of intolerance would never happen in a theocracy.

Or something like that.

Unless of course we are talking about something benevolent. In that case religion gets all the credit.

Alien in the sense of being different, non-conforming, and visibly not part of the vast majority. The Japanese-American citizens who were sent to the camps looked different, behaved differently, and worshiped differently. Despite many of them being native-born US citizens, they were treated as "aliens," and fear of what is different led to their imprisonment and confiscation of their property.

Chinese immigrants were excluded by law, as well.

If you are different, you are an "alien" in people's minds and therefore considered to be dangerous. This is a common pattern in human societies. We fear what we do not understand, and make very little effort to improve our understanding. The United States is no different from any other country in that regard, to our shame.

The history of the US is written with diversity. It's that diversity which made us strong. The problem is diversity eventually evolves into a national identity. This then subjects us to the same forces of demagoguery which so easily affect other nations with homogeneous populations.

However, we operate on the principle of majority rule, at least psychologically. What that means is that any identifiable minority group can be identified and demonized by the majority. That's also a part of our history, and it's not a pleasant part of our history to consider.

The tyranny of the majority is a real thing. It shouldn't exist, based on our founding principles, but does exist, due to the belief on some people's parts that the majority rules in all things. It's a paradoxical element in our society.