Final answer:
The Mier Expedition highlighted the tense and often hostile relationship between Texas and Mexico during a period of territorial disputes and national conflicts that contributed to the outbreak of the Mexican-American War.
Step-by-step explanation:
The Mier Expedition demonstrated the tense and often hostile relationship between Texas and Mexico. This was a period of heightened conflict that ensued after Texas's annexation by the United States in 1845, which was a significant factor in the outbreak of the Mexican-American War.
Such military expeditions and skirmishes were indicative of the strife regarding territorial claims, the boundary disputes, and the differing national interests between the two regions.