BAGRAM AIR FIELD, Afghanistan—President Barack Obama is telling troops in Afghanistan that Osama bin Laden got his justice one year ago, as the president stirs up memories of his signature foreign policy victory in a secret trip to this war zone.

Obama told the troops: "The reason America is safe is because of you."

The president hailed the agreement he just signed with Afghan President Hamid Karzai (HAH'-mihd KAHR'-zeye) in Kabul, calling it a responsible transition to Afghans taking control of their own country. He says the change won't happen overnight because the U.S. will not risk the gains so many have sacrificed to achieve.

Obama's surprise trip Tuesday to Afghanistan coincided with the one-year anniversary of the U.S. raid in Pakistan that killed bin Laden, the al-Qaida (al-KAH'-ee-duh) leader.