[fortheDeclaration]

The point is that the Mexicans certainly did not (rightly or wrongly) hold to the Rio Grande as being the boundry.

Thus, as far as they were concerned the border was still an open issue.

[GOPcapitalist]

The point is that the Mexicans certainly did not (rightly or wrongly) hold to the Rio Grande as being the boundry.

That point is irrelevant though because the Mexicans did not recognize Texas' independence at all after reneging on the treaty. The rest of the world did though, and when the Mexicans yet again attempted to invade Texas' territory Zachary Taylor was waiting there to stop them.