The Qing court banned the northeast from entering the customs, and people in the customs were not allowed to go out. Where does customs mean?

I think Guan refers to the north of Shanhaiguan. It is the land in our northeast today. And part of Russia was also our territory at that time. He's scared. The Han people in Shanhaiguan went to the outside of Shanhaiguan Pass, because the resources outside Shanhaiguan Pass were rich, and they lost their resources there. Another Manchu marriage besides Guan Yu made them sinicized. Therefore, people in the customs are forbidden to leave the customs.