Harry Truman decided to pay a visit to Mexico in 1947  the first time that a US President had done so. The following story comes from David McCullough's biography, Truman:

The crowds in Mexico City were such as Truman had never experienced. Hundreds of thousands of people poured into the streets to see and cheer an American President for the first time. The trip had been Truman's idea and the acclaim was thrilling. He returned the "Vivas!" of the throngs (one woman shouted, "Viva Missouri!"), and several times broke away from his Mexican and Secret Service escorts to shake hands with people. "I have never had such a welcome in my life," to told the Mexican legislature, to whom he pledged anew Roosevelt's Good Neighbor policy. To a crowd of American citizens later, he said he hoped they would remember that they, too, were ambassadors.

The next morning, he announced suddenly that he wished to make an unscheduled stop at Mexico City's historic Chapultepec Castle, where, with one simple, unheralded gesture, he did more to improve the Mexican-American relations than had any President in a century. Within hours, as the word spread, he had become a hero.

The long motorcade pulled into the shade of an ancient grove of trees. Truman stepped out of his black Lincoln and walked to a stone monument bearing the names of Los Niños Héroes, "the child heroes," six teenage cadets who had died in the Mexican-American War in 1847, when American troops stormed the castle. According to legend, five of the cadets had stabbed themselves, and a sixth jumped to his death from a parapet rather than surrender. As Truman approached, a contingent of blue-uniformed Mexican cadets stood at attention. As he placed a floral wreath at the foot of the monument, several of the cadets wept silently.

After bowing his head for a few minutes, Truman returned to the line of cars, where the Mexican chauffeurs were already shaking hands with their American passengers.

The story created an immediate sensation in the city, filling the papers with eight-column, banner headlines. "Rendering Homage to the Heroes of '47, Truman Heals an Old National Wound Forever," read one. "Friendship Began Today," said another. A cab driver told an American reporter, "To think that the most powerful man in the world would come and apologize." He wanted to cry himself, the driver said. A prominent Mexican engineer was quoted: "One hundred years of misunderstanding and bitterness wiped out by one man in one minute. This is the best neighbor policy."

President Truman, declared Mexican President Miguel Alemán, was "the new champion of solidarity and understanding among the American republics."

Asked by American reporters why he had gone to the monument, Truman said simply, "Brave men don't belong to any one country. I respect bravery wherever I see it."