COLLEVILLE-SUR-MER, France -- Men who stormed Normandy's shore 70 years ago joined world leaders Friday in paying tribute to the 150,000 Allied troops who risked and lost their lives in the D-Day landings in Nazi-occupied France, in a day of international commemorations of history's biggest amphibious invasion.
They are honoring the troops and civilians who fell in mighty battles that helped bring Europe peace and unity - just as bloodshed in Ukraine is posing new challenges to European security and threatening a new East-West divide.
[SLIDESHOW: D-Day commemorations, Thursday, June 5, 2014]
As the sun rose Friday over a gusty Omaha Beach, flags flew at half-staff. A U.S. military band played Taps, while D-Day veterans from the 29th Infantry Division and serving soldiers stood at attention at exactly 6:30 a.m., the moment on June 6, 1944, when Allied troops first waded ashore.
"Twenty-nine, let's go!" they shouted, then downed shots of Calvados, Normandy apple brandy.
Hundreds of Normandy residents and other onlookers applauded the veterans, then began forming a human chain on the beach.
World leaders and dignitaries including President Barack Obama and Queen Elizabeth II are converging on Normandy to honor the more than 150,000 American, British, Canadian and other Allied D-Day troops who risked and gave their lives to defeat Adolf Hitler's Third Reich.
The D-Day invasion was a turning point in World War II, cracking Hitler's western front as the Soviet troops made advances in the east. Overall at least 4,400 Allied troops were killed the first day, and many thousands more in the ensuing three-month Battle of Normandy, which brought the Allies to Paris to liberate the French capital from Nazi occupation.
Russian President Vladimir Putin is also in attendance, invited by French President Francois Hollande in a gesture toward the 27 million Soviet citizens killed in World War II.
The D-Day commemorations are also offering a moment to try to reconcile Russia and Ukraine, and Russia and the West.
Putin is meeting German Chancellor Angela Merkel in Deauville on the Normandy coast Friday morning, after meeting Hollande and British Prime Minister David Cameron on Thursday night. Ukraine's president-elect is also coming to Normandy, and there is hope he and Putin may meet, too.
The encounters marked the first time the isolated Russian leader has met Western leaders since pro-European protests in Kiev pushed out Ukraine's Russian-leaning president in February and Russia annexed the Crimean Peninsula.
Back in Normandy, several thousand veterans, family members and others gathered at the Normandy American Cemetery and Memorial, with its 9,387 white marble tombstones on a bluff overlooking the site of the battle's bloodiest fighting at Omaha Beach, the emotional centerpiece of pilgrimages to honor the men killed in Normandy.
Soldiers of 173rd Airborne brigade, the ceremony organizers, served as ushers, wearing maroon berets. For the ceremony, small U.S. and French flags were placed in the ground at each grave.
Obama declared June 6 a national remembrance day.
In a declaration Friday, he said, "Seventy years later, we pay tribute to the service members who secured a beachhead on an unforgiving shore - the patriots who, through their courage and sacrifice, changed the course of an entire century. Today, as we carry on the struggle for liberty and universal human rights, let us draw strength from a moment when free nations beat back the forces of oppression and gave new hope to the world."
In addition to the fallen troops, Allied bombardments killed an estimated 20,000 French civilians, and Hollande paid tribute to them Friday in Caen, which like many cities of Normandy was largely destroyed in the bombings.
France has only tentatively come to grips with the invasion's toll on civilians. The Allied bombings - especially the deadly onslaught in Normandy during the invasion launched on D-Day - were used as a propaganda tool by the Vichy government. But historians now believe that nearly as many French civilians died in Allied air raids as Britons during the German Blitz.
"No one knew that this day would be the first of one of the most ferocious battles of France. This battle was also a battle of civilians," Hollande said. He said Normandy's residents "helped the victory happen. They opened their doors to the liberators."
Ceremonies large and small are taking place across Normandy, ahead of an international summit on Friday in Ouistreham, a small port that was the site of a strategic battle on D-Day.
Today's conflicts are also on many minds at the D-Day commemorations.
Jeffrey McIllwain, professor at the San Diego State University school of public affairs, will lay a wreath on behalf of educators who have lost students to wars in Iraq and Afghanistan - himself included.
He, like many veterans and world leaders here, is concerned about keeping the memory of D-Day alive as the number of survivors dwindles.
He brought 12 students to Normandy for a course on the lessons of D-Day.
"I make them promise to bring their grandchildren to serve as a bridge to the next generation," he said.