As they always do, Russia's finest infantrymen, sailors and airmen strode across Red Square on Sunday for the annual Victory Day parade, accompanied by a customary display of intimidating weaponry. But this year, tradition was upended. There, in the shadow of the Kremlin, on ground that has long symbolized Russian might, marched a young soldier from Grand Street in Lower Manhattan, Spc. Tyler Smith, and his fellow Americans. Smith, 21, was in awe at playing a part in a momentous event: this year, American soldiers were invited to Victory Day, Russia's most important secular holiday, which commemorates the Soviet Union's triumph over Nazi Germany in World War II. Never before has this happened, the American military said. In interviews on Red Square, the Americans spoke of their pride in being asked to march, and the hope that their presence would help improve relations between the two countries In recent years, Victory Day has been something of a barometer of Russia's attitudes toward the West. When tensions have risen, Vladimir Putin, the prime minister and former president, has used his speeches to take aim at the United States. In 2007, he even seemed to suggest obliquely that American foreign policy was starting to have similarities to that of the Third Reich. This year, ties have warmed, as underscored by the invitations to troops from the United States, Britain and France -- known here as the anti-Hitler coalition. 'In 1945, not only a military but also a great moral victory was achieved,' Putin's protege, President Dmitry Medvedev, said at the parade. Still, not everyone was pleased that the boots of NATO soldiers were tramping over Red Square for the 65th anniversary celebration. Communists and nationalists have held protests, saying that these foreigners are, if not enemies, then certainly not friends. President Barack Obama, who is in part responsible for the better tenor of relations with the Kremlin, was invited but did not attend. Still, the Americans on Red Square were thrilled to be there. 'This is a world-changing event,' said Sgt. Mark Kupiec, 23, of Detroit. 'In years to come, they are going to be reading about this in the social studies books.' 