A Reminder of a Conflict That Faded Into History Alexandre Meneghini for The New York Times A museum in Saltillo, Mexico, is devoted to the Mexican-American War's Battle of Angostura. LA ANGOSTURA, Mexico - On the grassy, windswept hill where soldiers from north and south fought one of the most important battles of the Mexican-American War, the crunch and grind of a sand and gravel mine deafens any attempt at contemplation. Some wars get no respect. And this one, which Ulysses S. Grant called the most "wicked war" ever waged, has never been held in particularly high esteem. How many Arizonans condemning illegal border crossers want to recall that their homes sit on former Mexican territory? How many Mexicans want to remember the lost battle here, which they should have won? And yet, there are lessons here in these hills - for Mexico and the United States - that two Mexican history buffs are determined to teach. They have spent years collecting artifacts and are now pushing to preserve the site as historic, though not many seem to care. Their three-room museum in nearby Saltillo, opened in 2006, is usually as lonely as a funeral home between wakes, a tangible reminder of the complicated past many Americans and Mexicans have overlooked. "People don't know what happened here," said Reinaldo Rodríguez, 68, a retired government planner as tall and thin as a torch, pointing to a diorama of the battle in the museum, which sits behind the Saltillo cathedral. People don't know that this was the place where the Irish died alongside the Mexicans. The San Patricios, or St. Patrick's Brigade, they called themselves. They were all recent immigrants to the United States who had joined the American Army, then defected to fight with Mexico. Most were in fact Irish. Some came from Germany or England, and historians say they fled in disgust, fed up with one of the United States" ugliest flaws: prejudice. "One reason why so many people deserted was that they were Catholic and they felt like they were being mistreated by their Protestant officers," said Amy S. Greenberg, a historian at Pennsylvania State University. At the time, in the 1840s, many Americans saw Roman Catholics as an invading horde and a threat to American values. Hatred and discrimination were widespread, and in the military, historians note, rank reinforced bigotry: a majority of the full-time Army regulars were poor immigrants and Catholics, while officers and part-time volunteers were overwhelmingly wealthier white Protestants. The Mexican-American War also had little to do with principle - historians on both sides of the border describe it as little more than a land grab - and desertion was a problem even before the conflict started. As troops massed on the American side of the Rio Grande in 1845, scores of soldiers, including many immigrants, disappeared across the border. The San Patricios, whose numbers grew into the hundreds, became the most famous deserters. They made their first appearance as a unit in September 1846 at the Battle of Monterrey. "No one had ever seen people from another country, especially Europeans, come and help the Mexican Army," Mr. Rodríguez said. And they were tough, too. "They became the most effective fighting force that Mexico had, largely because they knew how to use the armaments of the U.S. Army," said Professor Greenberg, author of "A Wicked War: Polk, Clay, Lincoln, and the 1846 U.S. Invasion of Mexico." They had a special talent for capturing American cannons, she added, "and for using them against the Americans incredibly effectively." Here at the battle of La Angostura, which the Americans call the Battle of Buena Vista, the San Patricios occupied a spot near the base of the hillside, just below where the gravel mine can now be found. By most accounts, they pounded the Americans, and kept them from advancing for two days. But it was not enough. The Mexican commander, Gen. Antonio López de Santa Anna, retreated after the second day of battle on Feb. 23, 1847. His troops outnumbered the Americans three or four to one, and many historians argue that the Mexicans were defeating the ranks of volunteers and regulars led by Gen. Zachary Taylor, whose hero status in the war ultimately led him to the White House.