What happened to the land between the Sabine River and the Arroyo Hondo-Calcasieu line after the negotiations between Spain and the United States?

After the acquisition of the Territory by the United States, these not only claimed the same limits that the French had established, but were not recognized by Spain, but advocated its extension to the Rio Grande, although in fact they are limited to Sabine river, in front of the Spanish claims that put the limit in the Arroyo Hondo.

The negotiations were developed until its break in 1805, giving way to verbal and armed clashes between October 1805 and October 1806.2

Despite the tension, none of the contenders wanted an armed conflict, so the military governors of the area, Lieutenant General Simón de Herrera for Spain and General James Wilkinson for the United States, reached an informal agreement not to aggression and the establishment of a neutral strip on November 5, 1806, although the borders were not delimited. Although it does not acquire the category of formal Treaty, it was generally respected by both parties, except in the breach, by both, of the prohibition to establish new settlers.

The demilitarized strip was bounded between the Arroyo Hondo to the west and the Sabine river to the east. To the south it reached the Gulf of Mexico and the north was assumed (without specifying) the line of the parallel 32º

In 1819 the Adams-Onis Treaty was ratified in 1821, marking the limits of both states and the waiver of future claims. When in 1821 Mexico became independent, it assumed that Treaty.

When negotiations failed it first in 1805, after a little more than a year and due to the fact that none of the powers were keen to go to war over the land, it was established a neutral ground by U. S. General James Wilkinson and Spanish Lt. Col. Simón de Herrera, which was mainly respected even though clear borders were never defined.

That lasted until 1819 when The Adams-Onís Treaty, was signed and then ratified in 1821, recognizing the U. S. claim and thus setting the border at the Sabine River. It is important to notice that the Neutral Ground and the adjacent part of East Texas remained with Spain.

Spain surrendered any claim to the area, mainly because they had their own internal problems, so much so that two years after the treaty was negotiated, New Spain won its independence and became the Mexican Empire.