Mexico had permitted and even invited immigrants to part of its Northern territory. In the case of the Northeastern section of Mexico, those immigrants interacted and in a few cases intermarried with the existing inhabitants Northern Mexicanos and Indios. Although for the most part (like other Northern Mexican regions-today New Mexico , Colorado, California, Arizona, Nevada) the new Anglo immigrants kept themselves separate.
The land was vast and was part of the frontier (both qualities which could influence those who came). Central Mexico and the Mexican/Spanish government was far away and did not have much day to day influence.
Why did the Texas insurrection occur? Be careful here as I do not wish you to just copy what others think nor paraphrase textbooks or historians but think about the time period and the peoples involved and the condition of the Mexican and Spanish state as well as from where the Anglo settlers immigrated and the nature of the existing Tejanos (Northern Mexicanos).
Please examine the underlying factors. The immediate catalysts are not as important or even very important as the underlying factors. Who (what peoples) actually revolted? Who were the leaders of the Texas insurrection? Who led the opposition to the insurrection ( who in Texas as well as from central Mexico)? What economic , social and political goals were the basis for the actions on each side?
It is necessary here to conduct outside research from scholarly sources and to have read at least part of the Buenavida Dilemma.
Be aware that existing in western lower section of North America were hundreds of thousands of Northern Mexicanos prior to 1860 and that millions lived in the Western U.S. long before 1960. In other words, the roots of Northern Mexico and Mexico are deep but different and Anglos relatively recent to this area.
Remember also that Mexico had just started on the road of nation building ( as did the U.S., just prior to Mexico’s independence from Spain) and like other nation states was in the process of developing and various forms of governing were displayed. Santa Ana had a history with Mexico governance and was to surface again reflecting various movements.