U.S. President Barack Obama's historic Hiroshima visit Friday signifies a step forward in his stated 2009 dream of a "world without nuclear weapons."

Tokyo and Washington say Obama's trip offers a chance to recognize the tremendous suffering of innocent citizens caused by the U.S. nuclear attacks on Hiroshima and Nagasaki.

But Obama's trip also casts light on key questions, including why Japan has welcomed his visit without a formal apology, and how much Obama has accomplished toward his goal of nuclear disarmament amid increasing — and menacing — military buildups in China, North Korea and elsewhere.