Ok, here’s the real story that they won’t tell you in school. Up until 1964 there was a country, to the north of the US, called Canada. But when the US got into the space race with the USSR, NASA started to devise the Moon Landing conspiracy. NASA knew it was impossible to put men on the moon but wanted everyone to believe we did it. They needed a desolate place to film the fake moon landing and realized the Canadan tundra would work. So, they methodically removed all the people from Canada and moved them to Mexico. It took a few years. Then in 1969, NASA was free to film the moon landing in Canada and fool the world. 
Only problem, the Canadians want to go back home now. They are disquused as Mexicans and keep trying to get home by crossing the border betw Mexico and the US and going north from there. Sadly, the US gov thinks they are illegal immigrants and keeps sending them back to Mexico. 
So, there you go. The REAL story of Canada and the US immigration problem.