A fair number of wars that have been fought by the United States have been declared, at one time or another, to be "forgotten wars." Indeed a book about the Korean War even goes by that title, reflecting the relative interest by the public in that post WWII, pre Viet Nam, conflict. Some of these conflicts are forgotten indeed. Few seem to recall much about the Spanish American War, the Philippine Insurrection or the Banana Wars, for example. Of the forgotten wars, however, I'd place the Mexican War near the top.
Few people in the US know we ever fought Mexico, even fewer know why, and of those who do recall the war, most know next to nothing about it. Perhaps this lack of remembrance is somewhat intentional. The war doesn't fit in well with American wars, at least in the way it has commonly been interpreted. Generally regarded as an unwarranted war of aggression, an overly simplistic analysis of the conflict, it seems to be inconsistent with the generally defensive nature of American military endeavors, notwithstanding the Indian Wars.
The war is well worth studying, however, as it had an enormous impact both on the country, and on the US Army. An understanding of US history really cannot be arrived upon without an examination of the Mexican War.
Of the forgotten stories of a forgotten war is the fact that the Army had a huge desertion rate, and that a group of US troops deserted and served Mexico. An enormous controversy at the time, the story was quickly and intentionally forgotten, with the reasons basically buried by the Army, which did indeed apply the lessons learned and avoided repeating its mistakes in the Civil War. However, two recent books have been written on the topic, The Rogues March and Shamrock and Sword. "The Rogues March" is by far the better of the two.
This book examines the leader of the artillery unit formed from American deserters, John Riley, as well as the deserters themselves. In order to do this it also has to examine the country at this period of time, and the US Army as an institution. The author skillfully develops the thesis that harsh treatment of Irish and German immigrant troops, who were largely Catholic, by Army officers, ultimately predisposed some to desertion. Appeals by the Mexican government to these troops common religious background, combined with some unfortunate American newspaper appeals comparing the war in Mexico to an anti-Papal struggle, hardly aided the situation.
Examination of the harsh discipline of the era is indeed shocking, the makeup of the destitute Irish and German immigrants, and the Mexican appeal offering land and better treatment fascinating. Riley's story itself, to the extent known, is intriguing (he may have served as an artilleryman in the British Army prior to immigration). Also of interest is the fratricidal nature of the Mexican officer corps at this time, and the disregard for the condition of their own troops. Artillery is discussed in a very minor way, that branch having its moment in the sun during the Mexican War. US use of flying batteries, a sometimes forgotten employment of the horse in war, proved to be decisive in the conflict.
Finally, Stevens goes on to tell the reader what became of the deserters who were not captured in the war, completing the story. The captured, as would be expected, were largely executed after trial.