With that example of no national border, Mexico should have the right to come take back Texas, New Mexico, Arizona, and California. It’s probably breaking them to support all these refugees.
That would be a valid response, if Mexico truly did inhabit those U.S. territories for hundreds or thousands of years.
Do you know how long Mexico had possession of them? Mexico wasn’t even an official nation until around 1820. Spain gave their claimed territories to Mexico officially around that time.
In 1850, the United States became their official owner.
So Mexico, had that territory for 30 years. Not only that, it didn’t lift a finger to conquer any of it successfully throughout history.
Mexico tried to claim it in perpetuity, and the U.S. objected. We won it in battle. We even paid for it, in two different agreements.
The Kurds have lived in that region for hundreds or thousands of years.
Not comparable...
I know where you're going with this, but a bad analogy. The USA paid for that territory land from Mexico with cash and blood. Fair and square, bought from Mexico. We could have kept all of Mexico when we conquered Mexico City, but let them keep Mexico proper. We bought their northern territories in cash and forgave Mexican debt.