There is a reason why countries like Switzerland have such a insanely low amount of violent crime despite people owning guns in amounts that rival America. It's why they never have a lot of issues other countries do.
If you want to become a citizen you have to pay a lot of money. You have to fluently speak their language. You have to demonstrate a understanding of their customs and history. So in the end all Swiss citizens speak the same language and have similar customs.
People are more productive, happier, more content and more comfortable around others that are similar to them. If everyone has a unspoken understanding of even strangers, when everyone speaks the same language, when everyone looks similar you tend to have more comfortable people in a society.
That's the problem with America. We have people from allover the world with different religions, cultures, beliefs, morals, standards, values l, languages and so on and none of those people want to conform to America. They want America to conform to them and no one will back down.
I believe America was better when it almost entirely all whites, we all spoke English, Christianity was the major religion, we all had some measure of pride in America, we all understood basic American customs and so on.