The two-day Nuclear Security Summit in Washington brought 46 other nations and three major international agencies under one roof to sign a pledge to put highly enriched uranium under lock and key within four years to stop terrorists from creating a nuclear weapon. “Today is an opportunity, not simply to talk, but to act — not simply to make pledges, but to make real progress on the security of our people,” said Mr Obama. David Miliband, the Foreign Secretary, praised the president’s vision and leadership in establishing a “gold standard of what nuclear security means”. Ukraine and Chile have agreed...