President Biden and key U.S. allies were in Normandy Thursday to commemorate the 80th anniversary of the U.S.-led allied forces' D-Day invasion of Nazi-occupied France. The brazen air and sea invasion would mark the beginning of the end of World War II, leading to the defeat of Adolf Hitler's Nazi German forces in Europe less than a year later. 

Mr. Biden, French President Emmanuel Macron, British Prime Minister Rishi Sunak and Canadian Prime Minister Justin Trudeau were together to mark the most significant victory of the Western allies in the war, as well as the largest seaborne invasion in history. Mr. Biden is in France through the weekend for D-Day anniversary commemorations and plans to meet with leaders of key allies during his visit.

"What the allies did here 80 years ago, far surpassed anything we could have done on our own," Mr. Biden said in remarks Thursday. "Together, we won the war."

"The men who fought here became heroes — given an audacious mission, knowing the probability of dying was real," he said. "But they did it anyway, knowing without a doubt there are things worth fighting and dying for. Freedom, worth it. Democracy worth it. America worth it. Then, now and always."

Mr. Biden and first lady Jill Biden met WWII veterans one by one ahead of a memorial ceremony at the Normandy American Cemetery on Thursday, presenting each one with coins made to commemorate the D-Day anniversary. He chatted and joked with some of the men, asking about their hometowns, thanking them for their service and calling them the greatest generation ever.

The president delivered remarks Thursday at a commemoration ceremony that was also attended by members of Congress from both parties, including House Majority Leader Steve Scalise, House Democratic Leader Hakeem Jeffries, and speaker emerita Nancy Pelosi.

"On behalf of the American people and its Commander in Chief, it's the highest honor to be able to salute you here in Normandy. All of you. God love you," Mr. Biden said, addressing the WWII veterans in the audience.

The U.S. president quoted Britain's WWII leader Winston Churchill, saying he "called what happened here the greatest, most complicated operation ever," and adding that the entire world waited to see the outcome of the "great crusade to free Europe from tyranny."

Speaking about the tens of thousands of American men who poured onto Normandy's beaches that day, charging into a hail of gun and mortar fire, Mr. Biden said "it was estimated that 80% of them would be killed within hours. That was the estimate. But they were brave. They were resolute," and they got the job done. 

• What happened on D-Day? A timeline of June 6, 1944

"The men who fought here became heroes, not because they were the strongest our toughest or fiercest, although they were, but because they were given an audacious mission, knowing, every one of them knew, the probability of dying was real," Mr. Biden said. "But they did it anyway. They knew, beyond any doubt, there are things that are worth fighting and dying for. Freedom is worth it. Democracy is worth it. America is worth it. The world is worth it. Then, now and always." 

The president then pivoted to Russia's ongoing war in Ukraine, warning that "tyrants" of today were watching closely for cracks in the transatlantic NATO defense alliance that grew out of the WWII Allied forces. He said democracy was "more at risk now than at any point since World War II."

Describing Russia's invasion of Ukraine as the actions of a "tyrant intent on domination," Mr. Biden vowed that the U.S. and its European partners "will not bow down."

"We cannot surrender to the bullies, it is simply unthinkable. If we do, freedom will be subjugated, all Europe will be threatened," he said.

The president and first lady also laid a wreath at the cemetery to remember the fallen soldiers. 

The Bidens then joined other international leaders on Omaha Beach for an international service commemorating the operation, listening to orators read the letters of those who landed on the beach. Ukrainian President Volodymyr Zelenskyy was among the world leaders present Thursday. 

The June 6, 1944 D-Day operation, given the codename OVERLORD, sent five naval assault divisions to the beaches of Normandy, France. The invasion included 7,000 ships and landing craft operated by more than 195,000 naval personnel. More than 130,000 troops from the U.S., Great Britain and their allies landed on the shores. Many more followed, and their efforts helped lead to the defeat of German Nazi forces. 

Mr. Biden planned to give a speech on Friday at Normandy's Point du Hoc cliffs that would highlight the men who scaled those cliffs 80 years ago, democracy and the "dangers of isolationism," said national security adviser Jake Sullivan. In his speech, the president will draw a line from World War II to the formation of NATO to today, as war again haunts Europe, Sullivan said. 

On Saturday, the festivities will continue as Mr. Biden participates in a parade procession to the Elysee Palace. And on Sunday, the president will lay a wreath at the Aisne-Marne American Cemetery, where World War I veterans are buried.  

Among the allies Mr. Biden will meet with in France is Ukrainian President Volodymyr Zelenskyy, as Ukraine continues to suffer from Russia's onslaught.

The president is expected to have an "extended discussion" with Macron on a range of issues, including the Middle East, Ukraine, the Indo-Pacific, technology and clean energy, Sullivan said. Macron and Mr. Biden are scheduled to make a joint press appearance on Saturday, and Macron is hosting a state dinner for the president and first lady on Saturday. 

In 2018, then-President Donald Trump opted out of the trip to Normandy to commemorate the anniversary of D-Day while in Paris, citing bad weather, a move that drew intense criticism. 

Kristin Brown contributed to this report 

In:
• War
• World War II
• D-Day
• Nazi
• France
• Germany
• Canada

Kathryn Watson

Kathryn Watson is a politics reporter for CBS News Digital, based in Washington, D.C.