It's truly amazing what lengths you Lincoln cultists will go to in order to protect the reputation of Saint Abe - even to the point of defending Santa Anna's claim over Texas!
You can't possibly mean to dispute that the land was Mexico's to begin with. Therefore Texas' is the upstart claim.
Being the "upstart" claim has nothing to do with the situation. If Texas declared and won its independence, then Texas necessarily has a series of set and defined borders in which that independence holds true. Looking to the documents and treaties the time, the ONLY specified border to appear with consistency is the Rio Grande. Thus we must conclude it to be the border of Texas. Conversely, if you wish to deny that the Rio Grande is the border you must also necessarily deny that Texas legitimately declared and won its independence. Why? Because having a defined border is what defines a nation's independence from another and if you deny the ONLY stated border that is formally recorded, you deny the concept that Texas had a border, and thus that Texas was a nation, entirely. So which is it, Heyworth? Are you gonna accept what Texas and the world have accepted since 1836? Or are you going to continue your quixotic endeavor to protect the reputation of Saint Abe and deny Texas it's nationhood after 1836 all together?
Except that Santa Anna was a prisoner of war whose army had just been soundly defeated at the time he signed the document. Pretty much a textbook example of duress.
Nice try, but the laws of battle differ from the laws of a contract. By your same measure Napoleon should have still ruled France after those little episodes on the Bellepheron and St. Helena. But he didn't, and you know why? Because his condition was the product of a military capture. The most common example of this sort of thing happened when two warships engaged and one was taken. The losing captain gave his sword over to the winner signifying a surrender, at which point the winner took full possession and ownership of the loser's warship, threw the other captain in the brig for a while, and normally paroled him on shore somewhere. Under the Lincolnian argument, that losing captain could later come back and claim that he gave up his sword, and ship with it, under "duress" then sue to have the ship restored to him - a notion that is flat out absurd, as would be Napoleon filing suit against Britain to have his empire restored.
Except that the part of the treaty agreeing to send Santa Anna home was immediately violated when elements of the Texian army took him and threatened to shoot him.
Wrong. The treaty stipulated only for the "prompt return" of Santa Anna to Mexico without stipulating any specific time, other than it should happen soon. Though he was not immediately allowed to disembark, Santa Anna was released in short order to Washington, and from there back to Mexico. That some desired to detain him longer and even to shoot him (which would have been perfectly justified given his atrocities), the fact remains that it did not happen and Santa Anna got his promised release.
He was a prisoner from May 1836 until February 1837. Are you actually going to claim that he was the head of state of Mexico the entire time?
If I recall correctly, instability in Mexico (the entire country was basically in revolution against Santa Anna - he had been marching his army around putting them down one by one until he got to Texas, where he lost) gave rise to others claiming to be head of state and years of subsequent turmoil. Santa Anna was indisputably the head of state the day he signed the treaty however.
Look at Article 5: "The present return of General Santa Anna to Vera Cruz being indispensable for the purpose of effecting his solemn engagements, the Government of Texas will provide for his immediate embarkation for said port."
...and he was eventually released. It may not have been as "prompt" as one might intend or desire, but given that no specific or binding timeframe was stipulated, it was "prompt" enough.
I'm also curious as to how you reconcile the public treaty, which calls for Texas forces to not approach within five leagues of what you're claiming is their own border.
Very easily. It's a zone of neutrality that limits military engagement. There have been hundreds of treaties throughout the history of the world with similar stipulations against countries militarizing parts of their territory but by no means depriving them of that territory. The most famous and most notorious was the 1918 stipulation against Germany for militarizing the Rheinland, which Hitler violated before WWII.
The land was the Indians to begin with. Then Spain stole it. Then Mexico seceded from Spain. Then Texas seceded from Mexico. Then the US accepted Texas. Then Texas tried to secede from the US and failed. Now the Latinos are talking about Atzlan.
Whoever can take and hold the land owns it. Just ask Israel.
You keep using the word "prompt," but that doesn't appear anywhere in the treaty. "Immediate" does.