Seventy years ago this month, the United States dropped two atomic bombs on Japan. The human toll was horrific: The bombs, dropped on Nagasaki and Hiroshima, killed at least 100,000 people and possibly many more.
The bombs also altered the course of history. Historians often debate the role of the bombs in ending World War II. But beyond even that, they defined how the world thinks about nuclear weapons. The way the bombs were used defined nuclear weaponry in the global imagination, including in the minds of nuclear-armed leaders, and thus helped set how nuclear weapons have been used, and not used, ever since.
None of this is to argue for or against the bombings of Hiroshima and Nagasaki; few things could be more callous than to weigh the strategic pros and cons of killing more than 100,000 civilians. Rather, it is only to understand how these two bombs changed the course of history in ways that are still very much with us.
Without the bombs, it's not clear nuclear weapons would have been taboo
It was probably inevitable that at some point, there would be a first time nuclear weapons were used in war. But if the first-ever bombs had been dropped under different circumstances, deployed in a different way, then the way we think about nuclear weapons now could be very different. And that could make their role in war very different.
Today, we almost take for granted that nuclear weapons should never be used as "ordinary" weapons of war. The notion that the US might nuke, say, an ISIS base in Iraq seems at once horrifying and impossible to imagine. This is called the "nuclear taboo."
Nina Tannenwald, a political scientist at Brown University who studies this taboo, believes that no nuclear weapons have been used since Nagasaki because they have acquired a special moral opprobrium in the eyes of the world. Their use simply cannot be justified, by anyone.
Hiroshima and Nagasaki played a huge role in creating this stigma. "The 'demonstration effect' of the bomb did contribute to the shock and horror, to the sense of revulsion that later emerged among the public, and to the rise of a taboo and subsequent efforts to control the taboo," Tannenwald writes.
It's possible, as she admits, that this would have happened regardless of the circumstances of the first nuclear weapons use. But it's far from obvious.
The next time that nuclear weapons were almost used: Korea
The US, in a case that is widely studied for what it says about the nuclear taboo and how it came about, came very close to using nuclear weapons again, just six years after Nagasaki.
After China entered the Korean War in late 1950, and American troops were pushed back from their advances, General Douglas MacArthur, the American commander on the ground, demanded authority to use nuclear weapons against Chinese targets. In April 1951, Truman transferred nine nukes to US military control.
"The only practical use of this secret transfer was to position these weapons for possible strikes on the Asian mainland," Nathan Jennings, a US Army captain who teaches history at West Point, writes.
Yet Truman ultimately balked. Witnessing the aftermath of Hiroshima and Nagasaki had transformed his view of nuclear weapons.
"You have got to understand that this isn’t a military weapon," the president said in April 1948. "It is used to wipe out women and children and unarmed people, and not for military uses. So we have got to treat this differently from rifles and cannon and ordinary things like that."
Tannenwald believes that this moral revulsion is one of the key reasons Truman refused to use nuclear weapons in Korea. "For Truman, a personal moral abhorrence of such weapons operated as a powerful restraint" in Korea, she writes. It's hard not to look at this exchange between Truman and one of the joint chiefs, General Hoyt Vandenberg, before Chinese entry in the war and see why:
Vandenberg: "If the Chinese enter the war, this will mean the use of atomic weapons."
Truman: "Who told you that?"
Vandenberg: "That's part of our strategic doctrine."
Truman: "You are not going to put me in that position. You'd better go back and get yourself some more strategic doctrine!"
After President Eisenhower succeeded Truman, he looked much more actively for ways to use nuclear weapons in Korea. But he ultimately came to believe global public opinion was too hostile: The nuclear taboo, in other words, had started to take hold.
"One of the major factors inhibiting US leaders' resort to nuclear weapons after 1945 was their repeatedly stated concern about the terrible consequences that would arise if they used the bomb again on Asians," Tannenwald writes. "This inhibition would not have existed without a first use on Japan."
The Korean War was critical to establishing the nuclear taboo. The longer the world went without any nuclear use, the more abnormal, alien, and abhorrent nuclear weapons became. By the time of the Vietnam War, the taboo had been integrated into American and global thinking.
As William Burr and Jeffrey Kimball write in the Bulletin of the Atomic Scientists, this taboo was central in preventing the US from using nuclear weapons in Vietnam:
When challenger Senator Barry Goldwater and others called for the use of nuclear weapons in Vietnam during the 1964 presidential campaign, President Johnson explicitly cited the language of taboo: "For 19 perilous years no nation has loosed the atom against another. To do so ... would lead us down an uncertain path of blows and counterblows whose outcome none may know."
A CIA study about potential outcomes of nuclear use in Vietnam argued that it would cause a "fundamental revulsion that the US had broken the 20-year taboo on the use of nuclear weapons" and produce a "wave of fear and anger," with allies condemning the United States for "having dragged the world into a new and terrible phase of history." Such admonitions put a damper on any serious White House consideration of using nuclear weapons in Vietnam during Johnson's tenure, although some advisers entertained the notion.
If the bombings of Hiroshima and Nagasaki had not been so horrific, then the US might have felt it would be morally acceptable, and might not cause too much public outrage, to use nuclear weapons in the Korean War as well. And if it reached that decision in Korea, it might have reached it in Vietnam too.
We could have, in that case, ended up living in a world where nations considered it acceptable to use nuclear weapons in war, where it treated them as just a particularly terrible kind of bomb rather than as something categorically different.
Had that happened, it is both difficult and easy to imagine the consequences, the wars in which the nuclear powers might not have felt that nuclear weapons were off-limits: the French war in Algeria, the Soviet war in Afghanistan. What about Israel's wars with its neighbors? Would NATO have considered nuclear weapons in Yugoslavia, or against Iraq, or in Afghanistan? What would that world look like? Would the principle of mutually assured destruction that kept the Cold War cold have been a little weaker?
Thankfully, we don't live in that world. But without nuclear weapons' terrible first uses at Hiroshima and Nagasaki, this stigma might never have attached. Perhaps the only good thing that can be definitively said about Hiroshima and Nagasaki is that they have never happened again.