Answer:
1- The Texas border question persisted for about 2 decades.
2- The Mississippi River was considered the theoretical border for the Native Americans.
Explanation:
1- The Texas border question persisted since the Mexican independence in 1832 until the signing of the Treaty of Guadalupe Hidalgo, in 1848, at the end of the Mexican-American War.
Among the notable aspects of the treaty, the Rio Grande was established as the dividing line between Texas and Mexico, and the protection of civil and property rights of Mexicans who remained in the new US territory was stipulated.
2- In the time before independence, the British Government made available to the Indians the lands between the Appalachian Mountains and the Mississippi River. Therefore, this river became the Indian border, between the territories of the settlers and the territories of the tribes.