The only "ownership" of Texas that the Mexican government had was the same one that Cortez had when he landed on the shore and planted his flag, "I hereby claim in the name of God and the King of Spain, all lands north, south east and west as far as a Conquistador can lead a horse!".
Since the indigenous people's of Texas derived from northern tribes who themselves migrated from across the Bering Strait ten thousand years ago, not southern regions, neither the indigenous tribes of Mexico nor the Spanish had any rightful ancestral claim to those territories.
Since neither the Spanish nor the Mexicans established any significant infrastructure or population there (QED, they were easily defeated militarily by US/Mexican rebel forces) the fact that they could not defend their territory from invasion demonstrates that they were unworthy of dominion over them.
See, there is a Natural Law at work in the world which states effectively that the only nation which deserves to exercise dominion is one which can defend its borders from invasion. Mexico couldn't effectively defend it's claimed territory from even a rather facile military incursion, therefore, it didn't deserve to exercise dominion.
International conventions of border sovereignty did not exist at the time of the Mexican - American conflicts. So in the most literal sense, no international laws were broken and no "theft" of territory occurred in the annexing of southwestern U.S. territories from Mexican control.
If the US had not taken those lands, other nations (France, Britain, Russia) with significant footholds in California, the Gulf of Mexico and elsewhere from overseas, steadily gathering forces and resources focused on those regions, surely would have. Mexico did not have the resources either militarily nor logistically to exercise dominion or enforce security for the disputed territories.
Then, countless trillions of dollars of development by U.S. citizens and non-Mexican foreign investors built up and developed Texas and all of the other territories in the interim. Their value today is the result of more than a century of investment, hard work, military defense overseas and border enforcement realized through investment of U.S. blood and treasure.
So the value of all of that must be added into the deal, which of course, would leave Mexico again, deeply in the U.S. 's debt.
The worth and value of a state does not simply spring spontaneously out of the ground - it must be built. The value of millions of acres of undeveloped land has no comparison to the value of a flourishing, first-tier infrastructure and economic engine.
In all likelihood, if Mexico had by some miracle been able to retain possession and control of those territories despite the designs of other vastly more powerful, more wealthy and more militarily strong nations all around it, there is virtually no doubt that they would never have been able to develop the territories to anywhere near the level it maintains today.
But of course, being largely and increasingly detached from reality is the norm for far leftist mass media entities like the NYT. They will not let a small thing like reality get in the way of believing in the Karl-Marx-inspired Myth of Aztlan.
