In his speech in Hiroshima in 2016, President Obama stated that "it is not the fact of war that sets Hiroshima apart." What he means by this is that war itself is not unique or unusual in human history. Wars have been fought for thousands of years, and the destruction and suffering caused by war are sadly not uncommon.
What sets Hiroshima apart is the unique and devastating nature of the atomic bomb that was used there. The atomic bomb caused unprecedented destruction and suffering on a massive scale. It killed tens of thousands of people instantly, and many more died in the weeks and months that followed due to injuries, radiation sickness, and other illnesses.
President Obama supports this claim by noting the scale of the destruction caused by the atomic bomb. He describes the scenes of devastation and suffering that he witnessed when he visited the Peace Memorial Park in Hiroshima, and he emphasizes the importance of remembering the human cost of war.
In making this claim, President Obama is not making any assumptions about war itself. Rather, he is acknowledging the reality that war has been a part of human history for thousands of years, and that the destruction and suffering caused by war are unfortunately all too common. However, he is also emphasizing that the unique and devastating nature of the atomic bomb used in Hiroshima should serve as a reminder of the urgent need to prevent the use of nuclear weapons in the future.