Why did the United States build the US-Mexico border wall? What is this for?

From 1980s to 1990s, many Latin Americans began to flood into the United States via Mexico (besides Mexicans, there were also Colombia, Brazil, Cuba and so on). At this time, the American economy is booming and needs a lot of low-tech labor, such as moving big bricks and washing dishes. These Mexican immigrants try their best to stay in the United States, and when they come, they will not leave. Moreover, Latin America is an individual society. When a person comes to America, he will try his best to bring his whole family, even his hometown? Acquaintances? Children are brought into the United States in batches, whether legally or illegally. Do they want one? The whole family is neat? Yes