What Makes White Americans think they have a right to control immigration?

I am sorry, but this post make me laugh. Mexico has some the harshest immigration controls in North America. Why do Mexicans feel they have the right to prevent poeples from Central and South American from entering Mexico? You also completely gloss over the fact that much of Mexico, Central, and South America was also built on the backs of slaves. I am sure that the Mexican government would be more than willing to surrender its sovereignty if a tribe of Aztecs, Myans or Incas suddenly appeared and asked them to leave.