I had never fully understood what those words in the Marine Corps song really meant, until I read A Glorious Defeat: Mexico and Its War with the United States.
After a fitful start to the Mexican War, American soldiers ended up occupying Mexico City, in the heart of the country. Interestingly, the Mexican government, then re-located 100 miles north, pondered their options. One idea was to arm the peasants and begin a guerilla war. However, the elites thought so little of that idea, that an idea to surrender the entire country for annexation by the U.S. carried more weight.
The war ended with California, most of Arizona and all of New Mexico going to the U.S., along with the southern border of Texas being settled in America’s favor. The war also served gave combat experience to the generals on both sides of the Civil War.
Harry Truman was the first American president to visit Mexico City since the occupation in 1847. He laid a wreath at the monument to Los Ninos Heroes, 6 teenage cadets who had died defending Chapultepec Castle. As one Mexican engineer said at the time, “One hundred years of misunderstanding and bitterness wiped out by one man in one minute. This is the best neighbor policy.”