Illegal immigration into the United States across the USA-Mexico border has been a big hot-button issue in recent years.
As many people here may already know, a person from Mexico wishing to travel to the USA by land border is required to obtain a "Border Crossing Card", which requires the person to visit an American office and explain the reason for the travel to the USA and also to present evidence that the person has a life in Mexico to return to after a temporary visit to the USA.
If a person from Mexico wishes to permanently relocate to the USA, he is effectively prohibited from doing so unless he has a family member in the USA who may "sponsor" him, an employer in the USA who may "sponsor" him, or he has a special skill.
When it comes to public debate about illegal immigration, on the one side, you have people who want to deport illegal immigrants. On the other side, you have people who want to grant blanket amnesty to illegal immigrants and grant them visas. There are also many viewpoints in between.
Some opponents of the current system claim that the system that we have is a relatively new phenomenon; that in the past, people were allowed to freely travel between countries; that "passports" and "visas" served merely as official identification, not papers that people were required to possess to travel.
My question here is, "How has the enforcement (and attitude) toward the USA-Mexico border changed over time?