We are talking about the Texas Revolution of 1835.
Tejanos (mexicans from Texas) and American settlers on the region rised against the centralist government of Mexico, in opposition to the regime of President Antonio López de Santa Anna. In response to the local insurgents, Mexican Congress passed the Tornel Decree declaring that any foreigners fighting against mexican military "will be deemed pirates and dealt with as such, being citizens of no nation presently at war with the Republic and fighting under no recognized flag."
In addition, after the Mexican War of Independence, Texas had become part of Mexico, and under the Constitution of 1824, was granted only one seat in the state legislature. This was another big factor causing friction with the threat of an increasingly limited political autonomy. Finally, we can say the conflict ultimately benefited the U.S., that ended up absorbing Texas as their 28th state.
Hope this help!
