What is the song Fernando about?

The song seems to be about two Mexican soldiers who are reflecting back on their participation in the Mexican War (1846-48), defending Mexico's claim to the disputed area of Texas situated between the Rio Grande and Nueces River. The initial clash here with American forces under the leadership of General Zachary Taylor brought on the Mexican War in 1846. Two years later a defeated Mexico signed the Treaty of Guadalupe Hidalgo accepting Texas Annexation and surrendering New Mexico and California to the United States.