"The time for our leadership is now," Obama declared to members of Parliament, who for the first time gave an American president the honor of addressing them from the 900-year-old hall where great and gruesome moments in British history have played out.
"If we fail to meet that responsibility, who would take our place, and what kind of world would we pass on?" the president asked.
Tracing an arc from the allied soldiers who fought on the beaches of Normandy to the NATO-backed rebels now fighting in Benghazi, Libya, Obama argued that only the Western allies have the might and fortitude to promote and defend democracy around the globe.
Obama's message that the U.S. and Europe remain vital on the world stage is one he is sure to carry with him as he heads next to Deauville, France, for a two-day summit of the world's top industrial nations. In addition to pressing economic matters, leaders will focus there, too, on how to support democracy in the Middle East and North Africa in a time of upheaval and economic strains.
In London, Obama urged patience in Libya and with the ongoing war in Afghanistan. He also renewed his determination to push for peace in the Middle East and voiced confidence that democratic stirrings ultimately would prevail there and in North Africa as Western allies stand fast.
Libyan leader Moammar Gadhafi and his regime "need to understand that there will not be a let-up in the pressure that we are applying," Obama said at a news conference with British Prime Minister David Cameron earlier in the day. "I think we will ultimately be successful."
Obama's vision of a relevant and revitalized U.S.-European partnership was a welcome message for Western allies who at times have displayed nervousness that the president has focused on the growing influence of Asia at their expense.
"It was wonderful to have the president here offering such a clear and unambiguous reaffirmation of our relationship," said British Education Secretary Michael Gove, a key ally of Cameron.
Opposition Labor Party legislator Rachel Reeves tweeted after the 35-minute speech: "Feeling uplifted and proud."