ST..JOHNS (CBC) - Europeans and Americans must work together to protect their common security by tearing down the walls that divide them, U.S. presidential candidate Barack Obama told tens of thousands gathered in Berlin on Thursday during the first formal speech of his foreign tour.

"That is why the greatest danger of all is to allow new walls to divide us from one another," Obama said, speaking not far from where the Berlin Wall once split the city.

"The walls between old allies on either side of the Atlantic cannot stand. The walls between the countries with the most and those with the least cannot stand. The walls between races and tribes, natives and immigrants, Christians and Muslims and Jews cannot stand.

"These now are the walls we must tear down," Obama said, drawing loud applause from the massive crowd. Police spokesman Bernhard Schodrowski said the speech drew more than 200,000 people.

Obama said he had come to speak not as a presidential candidate, but as a proud citizen of the United States and a "fellow citizen of the world."

He referred repeatedly to the successful Berlin airlift by the Allies 60 years ago when the Russians wanted to blockade the Western part of the city by cutting off supplies. Obama said had the Soviets succeeded, "Communism would have marched across Europe" and a new World War could have begun.

Obama said that 60 years later, they are facing a new peril in the form of terrorism and that nations must summon the same spirit that led to the airlift.

"This is the moment when we must defeat terror and dry up the well of extremism that supports it," he said. "This threat is real, and we cannot shrink from our responsibility to combat it."

He spoke about Afghanistan and the need for U.S. and German troops to defeat the Taliban and al-Qaeda.

"My country and yours have a stake in seeing that NATO's first mission beyond Europe's borders is a success."

He only touched on Iraq, saying that despite past differences, the world should support Iraqis seeking to rebuild their lives.

Obama also said that Americans have made their "share of mistakes" and their actions around the world "have not lived up to our best intentions."

"But I also know how much I love America. I know that for more than two centuries, we have strived - at great cost and great sacrifice - to form a more perfect union, to seek with other nations a more hopeful world."

Obama arrived in the German capital Thursday morning for the European leg of his tour after talks in the Middle East and Afghanistan and met with German Chancellor Angela Merkel, ahead of his speech in Tiergarten park.

The speech is considered a symbolic one, as several U.S. presidents, including John F. Kennedy, Ronald Reagan and Bill Clinton, made significant addresses in Berlin.

Obama had initially planned to hold the speech at the Brandenburg Gate, the famous landmark where the presidents made their speeches.

But that was opposed by Merkel, who indicated she believed the site, which stood for 28 years behind the Berlin Wall in communist East Germany's heavily fortified border zone, was reserved for elected U.S. presidents, not candidates.

On Wednesday, Merkel told reporters she planned to talk about climate change and global free trade with Obama, and made it clear that Germany will stand by its refusal to send combat troops to southern Afghanistan.

Former German president Richard von Weizsaecker said the Obama event could help pave the way for a new transatlantic relationship.

"Kennedy said the famous sentence, 'Ich bin ein Berliner,"' von Weizsaecker told the Bild newspaper. "Obama could send the Berlin signal: America is counting on Europe for its future.

"We have long believed that nobody in America is interested in our continent anymore," von Weizsaecker added. "The appearance and the speech of Barack Obama are evidence that this preconception is false."

Berlin is the first stop on a whirlwind European tour will also take the presumptive Democratic nominee to France and Britain in an effort to shore up his foreign credentials.

With files from the Associated Press

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