Besides the land in question belonged to Spain --- which invited white Americans in and gave land grants to them which are still honored by the USA government. Mexico declared it's independence from Spain and was so unable to rule that it hung onto the northern territories for only something like 25 years. Mexico has been a mess ever since it's independence, it still has no ability for self-rule.
That is very true!! What mexicans claim to be their own, they got (through a revolution) from Spain who took it from Indians. We've had possession of those lands a lot longer than Mexico.
But what gives someone the right to claim a land as its own? It is one thing and one thing only - your ability to defend it!! But we cannot be complacent in our military superiority. There's other ways to take over territory besides military force. One other way is through the power of demographics. And guess what folks?? Mexicans will soon be a majority in most southwestern states!! And with their vote they can take over.
The original con job.
The land never "belonged" to Spain in any real sense; it was only printing on bad maps and the wishful thinking of a self-impressed, but historically irrelevant society -- the Spaniard Conquistdors and their descendants. The pitiful attempt at colonization by baptism of the Indians in California and sustained, but numerically small settlements north of the Rio Brazos, merely points out the irrelevancy of their 3 centuries of "ownership" of the land that is now referred to as the Southwest.
Spain did not "own" the land north to the pole, even though the Pope may have declared it so; Mexico could not "inherit" what Nueva Espana never had; and the United States did the right thing in 1846 by securing both coasts against monarchial domination by any European power. History has proven that this was one of the best things to have ever happened.
The present mass exodus from the glaring failure country of the Americas threatens to end the shining achievement of the greatest success story in history, the country known as the United States.
"Anglos" began settling in Texas in large numbers in, correct me if I am wrong, the 1820s. They did more to develop Texas in 10 years than the Spanish and Mexicans did in 300. You are also correct about the fact that Mexico still has no ability for self-rule.