It's the invasion of the invaded. They come from lands where conquering colonial troops and punishing military expeditions have disembarked 1,001 times. Now this voyage in reverse isn't made by soldiers obliged to kill but by workers obliged to sell themselves in Europe or North America at whatever price they get. They come from Africa, Asia, and Latin America, and, since the burial of bureaucratic power, from Eastern Europe as well. In the years of the great European and North American economic expansion, growing prosperity required more and more labor, and it didn't matter that those hands were foreign, as long as they worked hard and charged little.
Poor immigrants do the hardest, poorest paid work in the fields and on the streets.
After work comes the danger. No magic ink can make them invisible. Paradoxically, while workers from the South migrate North, or at least risk the attempt against all odds, many factories from the North migrate South. Money and people pass each other in the night. Wherever money travels, it's greeted with kisses and flowers and fanfare.