Kerry at the Hiroshima Peace memorial Park [View all]
From the descriptions from many news sources, Kerry very deftly threaded a needle here - displaying compassion for those who died, without getting into anything that could be seen as apologizing for the US. While speaking of hope that the world could in the future eliminate nuclear weapons, his strongest comments speak against war itself .. not a specific weapon. It is fitting at a gathering of foreign ministers that one speaks of using diplomacy to avoid war. Though likely not planned, the photo of Kerry and the Hiroshima born Japanese foreign minister together under the arch is a strong image that encapsulates the message of Japan and the US now being strong allies.
The BBC had a detailed article that included the above photo - http://www.bbc.com/news/world-asia-36012206
ABC showed the message he left in the guide book.
He later tweeted out a photo of his message, which reads: "Everyone in the world should see and feel the power of this memorial. It is a stark, harsh, compelling reminder not only of our obligation to end the threat of nuclear weapons, but to rededicate all our effort to avoid war itself. War must be the last resort - never the first choice. This memorial compels us all to redouble our efforts to change the world, to find peace and build the future so yearned for by citizens everywhere."
http://abcnews.go.com/International/kerry-makes-gut-wrenching-visit-hiroshima-memorial/story?id=38304368