The world first observed the phenomenon of mass destruction during the last days of World War II in August 1945 when Hiroshima and Nagasaki were hit by two nuclear bombs. The nuclear bomb had never been tested before, and for the first time it was tested during World War II. Human beings and infrastructure at Ground Zero immediately vanished. After these nuclear bombings, the word “nuclear” stirred up an alarming fright. On August 6, 1945, the first nuclear bomb named Little Boy was dropped on Hiroshima by the US aircraft. President Harry S Truman announced the next day that the bomb was more powerful than 20,000 tons of TNT. The nuclear bomb was dropped at an altitude of about 600 metres above the ground to assure maximum devastation. The city had military centres and industries in abundance. The destruction was unthinkable; almost 80 percent of the city vanished away. Every house in the city was demolished or burned. It was a uranium bomb that was dropped on Hiroshima, and at the time of blast, the temperature at the hub of fireball was 50,000 degrees. The temperature on the ground (below 600m from the fireball) was approximately 4,000 degrees centigrade. It is estimated that about 350,000 people resided in Hiroshima, and there were about 76,000 buildings at that time. When the bomb was dropped, 80,000 people instantly died while 140,000 died in the next few months. Everything within the radius of 2,000 metres was entirely wiped out, while the damaged area was estimated to be 13,250,000 square metres. On August 9, 1945, the second bomb named Fat Boy was dropped on Nagasaki. The Nagasaki was an industrialised city with some important ports. The bomb was dropped at an altitude of about 500 metres above the ground, and it was more powerful than 22 kilotons of TNT. The bomb that was dropped on Nagasaki was a plutonium bomb. In Nagasaki, about 270,000 people were living at the time of explosion. When the nuclear bomb was dropped, about 74,000 people died immediately. The instant casualties in both cities were around 200,000, while more people lost their lives due to wounds or various diseases, and many others lived with lifetime disabilities. As due to immediate and short-term causes of radiations, 15-20 percent lost lives due to radiation sickness; 20-30 percent died because of fire burns; and 50-60 percent was killed from other injuries. In total, about 300,000 people were exposed to radiation. Moreover, other loss included high damage to infrastructure and environment, while long-term effects still continue. The subject of a nuclear war has changed in recent years as compared to the cold war because the technological and political environment has changed. The nuclear danger has shifted from quantity to quality. Now nuclear bombs are more powerful than those dropped on Japan in 1945. The nuclear war or the danger of dropping a nuclear weapon on another state is interrelated to the number of countries having nuclear arsenals, which are increasing in the 21st century. In addition to P5, Pakistan, India, Israel and North Korea became nuclear weapon states. Iran is also likely to enter into the nuclear club in a decade or more. Moreover, it is opined that those having civil nuclear programme also posses the potential to produce a nuclear bomb in the future. The increase in number of countries possessing nuclear technology reinforced the debate about the dangers of a nuclear war. McGeorge Bundy, President John F Kennedy’s national security advisor, said in 1969: “Any decision that results in even a single hydrogen bomb explosion on one city of one’s own country would be declared as a calamitous mistake; while explosion of 10 bombs on 10 cities will be resulted as a tragedy far beyond history, whereas a 100 bombs on a 100 cities are beyond imagination.” The interdependency of intentions and capability between nuclear states makes the nuclear crisis harder to handle than a conventional war, and this is what happened in the Cuban Missile Crisis. In WWI, about 20 million people were killed, and the killings in WWII doubled and tripled this number. After both world wars, humanity was restored, but the horrors of wars prevailed. General Douglas MacArthur said in 1960s: “A World War will wipe out both sides; if you lose you will be destroyed and if you win you stand to lose. In either case it is double suicide.” Similar views were expressed by a former US secretary of defence, “If deterrence fails and crisis emerge the whole western civilisation will be annihilated.” Many researches presume that the deaths in WWIII are unthinkable. In addition to that, millions will die due to injuries, radiation effects and lack of medical assistance. Other than human killings, the ecological concerns are high in such a scenario, as scientists believe that a firestorm caused by a nuclear explosion can lead to a nuclear winter that can erase homo sapiens from earth forever. The recent studies says that even a limited nuclear war between Pakistan and India would be a threat to the entire region, and would result in devastating ecological aftereffects due to ash and firestorms on urbanised cities. History is full of wars, but the aftermath of a nuclear war — accidental or escalating — or dropping a nuclear bomb — advertent or inadvertent — would be unthinkably catastrophic. Thus those states that threaten each other with nuclear weapons and spend big chunks of their budgets on a nuclear arms race need to think the unthinkable on the 71st anniversary of Hiroshima and Nagasaki A-bombings. The writer is a member of an Islamabad-based think tank Strategic Vision Institute. She works on issues related to nuclear non-proliferation and South Asian nuclear equation, and writes for national and international publications