Answer:
First, there is the annexation of Texas which was an initial lost of territory for Mexico in 1845, or at least it became formal. The ensuing Mexican-American War (1846-1848) started as a border conflict, but its outcome accomplished the great goal of westard expansion to the shores of the Pacific Ocean that is part of the Manifest Destiny doctrine. Besides, it added millions of square miles to the territory of the US.
Explanation: