Answer:
The Americans
Explanation / Resources:
"The United States received the disputed Texan territory, as well as New Mexico territory and California. The Mexican government was paid $15 million — the same sum issued to France for the Louisiana Territory. The United States Army won a grand victory." (www.ushistory.org)
"The Mexican-American War was a conflict between the United States and Mexico, fought from April 1846 to February 1848. Won by the Americans" (www.britannica.com)