The American population of Mexican Texas: invasion or invited immigration...

In 1821 Mexico achieved independence from Spain.
Texas, with a total population of 3,000, contained only three outposts of Spanish civilization.  These settlements, Neches, Goliad, and San Antonio de Bexar, were remote from Mexico City and were maintained with difficulty against the raids of marauding Indians.
In an effort to populate Texas, Mexico offered land in generous tracts to foreigners, virtually free, in three successive colonization laws of the years 1823, 1824, and 1825.  One of the only requirements imposed on immigrants were those of religion; immigrants had to be, or become, Roman Catholics. 
Clauses in the colonization laws offered inducements; exemptions of foreigners from all taxes for a period of four years.  Further special inducements were added; colonists were given exemption from state and local taxes for a period of ten years. 
The colonization system was expected to develop Texas while eventually enriching Mexico while also serving as a buffer, protecting the southern Mexican states from raids by Indians of the Great Plains.
Only Americans came to Texas in substantial numbers.  Mexicans were not of pioneering stock; they were reluctant to run the risks of Indian dangers of the Texas frontier.  In 1830 not more than 4,000 native Mexicans were settled in Texas, all in or near the three established settlements.  In 1830 there were over 25,000 Americans in Texas.
The Mexican Congress, in alarm, on April 6, 1830 adopted a law prohibiting any further American colonization.  But the law proved a failure.  The Mexican Treasury lacked enforcement money and the Administration was feeble and inept.  The flow of Americans into Texas continued after 1830 almost as if no restrictions had been imposed.  The most important result of the law was a growing friction between the Americans already in Texas and the Mexican government.
A main source of discord was the status of Texas in the Mexican federation.  The Texans, as their numbers grew, demanded separate statehood.  Texas tariff exemptions had also expired in 1830.
The first major uprising occurred in 1832...

History of the Westward Movement
by Frederick Merk