Final answer:
Spain and later Mexico required Texas as a buffer to increase population, protect against Native American tribes, and act as a bulwark against American expansion. Settlement policies facilitated American immigration, but conflicts over slavery and loyalty to Mexican laws led to Texas's independence and eventual U.S. annexation.
Step-by-step explanation:
Spain, and later Mexico, needed Texas as a buffer province to fulfill multiple strategic purposes. Initially, Spain encouraged empresarios to settle in Texas to create a demographic barrier between its colonies and the Native American tribes, as well as to serve as a safeguard against possible American expansion. Following the Adams-Onís Treaty, which set the U.S.-Mexico boundary in 1819, American settlers began to move into northern Mexico, with clear intentions of taking this vulnerable land for the expansion of the United States. When Mexico gained independence in 1821, it continued the policy of promoting settlement to populate Texas and protect its other territories.
Colonization laws were enacted to facilitate immigration, hoping that non-Native settlers would also serve as a defense against Native American tribes and further consolidate the region under Mexican sovereignty. The government also hoped that by populating Texas with settlers who were sympathetic to Mexican laws, including the abolition of slavery, they could fortify the region against encroachment by American expansionists. However, the settlers from the U.S., many of whom were coming from slave states, had different intentions. They flocked to Texas, outnumbered the Tejanos, and did not adhere to Mexican laws, particularly regarding slavery. This tension ultimately led to the Texas Revolution, the establishment of an independent Texas, and its eventual annexation by the United States.