Their surrender of Louisiana was due primarily to the steady pushing and crowding of the frontiersmen, and the continuous growth of the Western commonwealths.

In spite of Pinckney's treaty the Spaniards did not leave Natchez until fairly drowned out by the American settlers and soldiers.
They now felt the same pressure upon them in New Orleans; it was growing steadily and was fast becoming intolerable.

Year by year, almost month by month, they saw the numbers of their foes increase, and saw them settle more and more thickly in places from which it would be easy to strike New Orleans.

Year by year the offensive power of the Americans increased in more than arithmetical ratio as against Louisiana.
Incursions of American Adventurers.
The more reckless and lawless adventurers from time to time pushed southwest, even toward the borders of Texas and New Mexico, and strove to form little settlements, keeping the Spanish Governors and Intendants in a constant fume of anxiety.

One of these settlements was founded by Philip Nolan, a man whom rumor had connected with Wilkinson's intrigues, and who, like many another lawless trader of the day, was always dreaming of empires to be carved from, or wealth to be won in, the golden Spanish realms.