"Peace with justice means pursuing the security of a world without nuclear weapons, no matter how distant that dream may be," Obama said. "And so as president, I've strengthened our efforts to stop the spread of nuclear weapons and reduce the number and role of America's nuclear weapons. Because of the New START Treaty, we're on track to cut American and Russian deployed nuclear warheads to their lowest levels since the 1950s."
But more work must be done, he said and announced additional steps.
After a comprehensive review, I've determined that we can ensure the security of America and our allies -- and maintain a strong and credible strategic deterrent -- while reducing our deployed strategic nuclear weapons by up to one-third," said Obama, who shed his coat early on in his speech under warm, sunny skies. "And I intend to seek negotiated cuts with Russia to move beyond Cold War nuclear postures."
He said the United States would work with its NATO allies "to seek bold reductions in U.S. and Russian tactical weapons in Europe. And we can forge a new international framework for peaceful nuclear power, reject the nuclear weaponization that North Korea and Iran may be seeking."
Obama also announced the United States will hold a summit in 2016 "to continue our efforts to secure nuclear materials around the world, and we will work to build support in the United States to ratify the Comprehensive Nuclear Test Ban Treaty and call on all nations to begin negotiations on a treaty that ends the production of fissile materials for nuclear weapons."
"These are steps we can take to create a world of peace with justice," he said.
Peppering his speech with the phrase, "peace with justice," Obama also spoke of efforts to tackle climate change, close the military prison at Guantanamo Bay, Cuba, eradicate AIDS and treat all persons equally.
"We are more free when all people can pursue their own happiness," Obama said. "As long as walls exist in our hearts to separate us from those who don't look like us or think like us or worship as we do, then we're going to have to work harder together to bring those walls of division down."
He also spoke about the need to balance national security with personal privacy, addressing controversies over the National Security Administration's cellphone and Internet monitoring.
"[Peace] with justice depends on our ability to sustain both the security of our societies and the openness that defines them, Obama said, later noting, "which is why even as we remain vigilant about the threat of terrorism, we must move beyond the mind-set of perpetual war."
In America it means "redoubling our efforts" to close the prison at Guantanamo Bay and controlling the use of new technologies such as drones, he said.
"It means balancing the pursuit of security with the protection of privacy. And I'm confident that that balance can be struck," Obama said. "I'm confident that, working with Germany, we can keep each other safe while at the same time maintaining those essential values for which we fought."
The U.S. programs are "focused on threats to our security, not the communications of ordinary persons. They help confront real dangers, and they keep people safe here in the United States and here in Europe."
During a joint news conference at the Chancellery, German Chancellor Angela Merkel said she and Obama discussed the public's concern about "some kind of blanket, across-the-board gathering of information."
"[There] needs to be a balance; there needs to be proportionality, obviously, between upholding security and safety of our people and our country -- and there are quite a lot of instances where we were getting very important information from the United States," she said.
"And at the same time, obviously people want to use those new, modern means of communication and technology and do so freely," she said. "And as we learn to live and deal responsibly with other new means of technology, we have to learn and deal responsibly with this one."
Obama said during the news conference he told Merkel a balance must be struck "and we do have to be cautious about how our governments are operating when it comes to intelligence."
Once he returns to the United States, Obama told reporters, he will look for ways "to declassify further some of these programs without completely compromising their effectiveness, sharing that information with the public, and also our intelligence teams are directed to work very closely with our German intelligence counterparts so that they have clarity and assurance that they're not being abused."
At Brandenburg Gate, Obama said all democratic governments must listen to the "voices who disagree with us" and have an open debate about "how we use our powers and how we must constrain them."
Democracies also must remember "that government exists to serve the power of the individual, and not the other way around," he said. "That's what makes us who we are and that's what makes us different from those on the other side of a wall."
The Berlin Wall belongs to history, he said, "And the greatest tribute that we can pay to those who came before us is by carrying on their work to pursue peace and justice not only in our countries but for all mankind."
Fifty years ago next week, President John F. Kennedy spoke at the Brandenburg Gate about democracy versus communism.
"Freedom has many difficulties, and democracy is not perfect," he said. "But we have never had to put a wall up to keep our people in, to prevent them from leaving us," referring to the Berlin Wall, built in 1961 and torn down in 1990.
Kennedy's Jan. 26, 1963, speech is known for a phrase he said in German: "Ich bin ein Berliner," or "I am a citizen of Berlin."
"General-Secretary Gorbachev, if you seek peace, if you seek prosperity for the Soviet Union and Eastern Europe, if you seek liberalization, come here to this gate!" Reagan said. "Mr. Gorbachev, open this gate! Mr. Gorbachev, tear down this wall!"
Notable deaths of 2014 [PHOTOS]