Final answer:
U.S. troops were unsuccessful in keeping settlers off Native American lands in Texas due to the settlers' push for expansion, cultural independence, and neglect of Mexican laws, especially regarding slavery. The Battle of the Alamo escalated American involvement, making peaceful resolutions difficult.
Step-by-step explanation:
The troops sent by the United States to Texas to help keep settlers off Native American lands were unsuccessful for several reasons. The American settlers' steadfast desire for expansion, their cultural and social independence, and their blatant disregard for Mexican laws and treaties with Native Americans led to sustained conflict. Despite efforts by both Mexican and Native American forces to stem the tide of American settlement, the allure of land and economic opportunity in Texas was compelling.
Moreover, cultural differences and the issue of slavery exacerbated tensions between settlers and natives. American settlers often did not integrate into Mexican society, failed to adopt the Catholic faith as required, and flouted Mexican laws against slavery, ultimately leading to political and military clashes. The infamous Battle of the Alamo, among others, catalyzed further American support and involvement in Texas, demonstrating the complex interplay of social, cultural, and political factors that rendered the troops’ mission unsuccessful.