How did illegal immigrants enter a country and what did the national army do?

The first way is smuggling, which mainly includes smuggling from borders, high seas and transportation logistics routes, which is beyond the control of the general national army. For example, the border police in China are generally border guards, the marine police are on the high seas, and the inspection logistics are at the customs.

The second type is those who don't return after the deadline and enter the country with legal passports and visas, but refuse to return home after the visa expires, and some tear up their passports as soon as they get off the plane, which is beyond the control of the army.