Barack Obama is expected to call on Europe to do more in hotspots like Afghanistan when he speaks in Berlin later today in his only formal address of a week-long foreign tour.
His outdoor address is likely to draw tens of thousands of people.
Mr Obama held talks with German Chancellor Angela Merkel after arriving in the German capital this morning.
He will speak at the "Victory Column" in Berlin's Tiergarten park this evening. In the 45-minute open-air appearance, Mr Obama will ask Europe to shoulder more of the burden to help deal with global security threats.
"Hopefully (the speech) will be viewed as a substantive articulation of the relationship I'd like to see between the United States and Europe," Mr Obama told reporters in Israel shortly before leaving for Germany.
"I'm hoping to communicate across the Atlantic the value of that relationship and how we need to build on it."
Relations between the United States and Germany reached a post-war low under Merkel's predecessor Gerhard Schroeder, who strongly opposed the U.S. invasion of Iraq in 2003.
But the conservative Merkel, who grew up behind the Wall in the communist East, has worked hard to repair ties and emerged as one of President George W. Bush's closest allies in Europe.
She said on the eve of Mr Obama's visit that she expected to discuss NATO cooperation, climate change and trade issues with the Illinois senator during a morning meeting at the Chancellery that German officials have said will last about an hour.
They are also expected to discuss Afghanistan and Iraq, the countries where Mr Obama started his Middle East and European tour.
The Obama visit has dominated the newspaper headlines in Germany for weeks, even sparking sharp exchanges between Merkel and her foreign minister over whether a speech at the Brandenburg Gate was appropriate.
Merkel has said the landmark, where President Ronald Reagan famously urged Soviet leader Mikhail Gorbachev to "tear down this wall," is a place for presidents, not candidates to speak. Her advisers tried to convince the Obama campaign to hold the speech at a university or other low-key location.
Asked if he had read the Cold War speeches delivered by Reagan and Kennedy in Berlin to prepare for his own trip, Mr Obama said unlike the two presidents, he was just "a citizen".
"Obviously, Berlin is representative of the extraordinary success of the post-war efforts to bring the continent and to bring the West together," he said.
Reuters