Hong Kong is a migration issue. So there is a lot for the US and the rest of the world to learn there. A lot of mainland Chinese are working in Hong Kong and this has put increasing pressure on property prices as well as depressed wages. Hong Kong has extreme income and wealth inequality so what you are seeing there is a place at its breaking point. I don't know for sure but I am guessing it's probably challenging for a Hong Kong resident to leave and work in China, you probably need a visa and a work permit. In addition they would be giving up some of their freedom by doing so. And if you are unskilled labor I imagine that is even more difficult to do so.

Brazil also has massive income inequality. They have rising crime and a failing economy which lead to the rise of Bolsonaro. Reading about Bolsonaro and his rise to power is quite illuminating. A conservative authoritarian wave has been building since the 1970s world wide. Also his electorate where mainly influenced millennials which is really troubling. They basically responded to an idea/ideology without thinking things through.

In the US the border crisis is largely manufactured. Yes, people are coming here. They are escaping worse situations at home, seeking a better life for themselves and their kids. The previous policy was "catch and release" sounds bad but 90% of the undocumented immigrants continued to appear and processed through the system. Families were not separated and these people mostly went to family and friends already in the US and had support. Some could work pending their court appearances. That is the most American response to have, let people work! Putting them in cages helps no-one but the for profit prison industry.

We also see large examples of whole industries where immigrants are necessary to keep food prices low. The examples here are restaurants and food processors as well as in farming. So if there is a demand for these workers we should have a work visa system where people can earn their way in. We could say hey no more, but you will get inflation (if you raise wages... but even then there are no Americans who want to do the work) or a contraction. New businesses won't be able to develop at all. My guess is that industry will demand that the prison labor population be used to maintain competitiveness. The problem with the work visa approach though is that over time these folks will want representation (either unionization). So there is a lot of pressure to keep people undocumented.

Brexit is also about immigration and housing costs as well.