Obama's Nuclear Security Summit (PHOTOS)

President Barack Obama called on world leaders “not simply to talk, but to act” to secure or destroy vulnerable stockpiles of nuclear materials. Mr. Obama, addressing a plenary session of the 47-nation nuclear security conference he had convened here, told fellow leaders Tuesday morning that it was time “not simply to make pledges, but to make real progress for the security of our people.”

“All this, in turn, requires something else, something more fundamental,” Mr. Obama continued. “It requires a new mindset — that we summon the will, as nations, as partners, to do what this moment in history demands.”