The most thing that i fear and worried in this world,is a nuclear warfare.

Nuclear warfare (sometimes atomic warfare or thermonuclear warfare), is a military conflict or political strategy in which nuclear weaponry is used to inflict damage on an opponent. Compared to conventional warfare, nuclear warfare can be vastly more destructive in range and extent of damage, and in a much shorter time scale. A major nuclear exchange could have severe long-term effects, primarily from radiation release, but also from the production of high levels of atmospheric pollution leading to a "nuclear winter" that could last for decades, centuries, or even millennia after the initial attack.A large nuclear war is considered to bear existential risk for civilization on Earth.
Only two nuclear weapons have been used in the course of warfare, both by the United States near the end of World War II. On August 6, 1945, a uranium gun-type device (code name "Little Boy") was detonated over the Japanese city of Hiroshima. Three days later, on August 9, a plutonium implosion-type device (code name "Fat Man") was exploded over Nagasaki, Japan. These two bombings resulted in the deaths of approximately 200,000 Japanese people (mostly civilians) from acute injuries sustained in the detonations.
After World War II, nuclear weapons were also developed by the Soviet Union (1940s), the United Kingdom and France (1950s), and the People's Republic of China (1960's), which contributed to the state of conflict and extreme tension that became known as the Cold War. In the 1970s, India, and in the 1990s, Pakistan, two countries that were openly hostile toward each other, developed nuclear weapons. Israel (1960s) and North Korea (2000s) are also thought to have developed stocks of nuclear weapons, and have made the political decision to retain them to the present time. South Africa also manufactured several complete nuclear weapons in the 1980s, but subsequently became the first country to voluntarily destroy their domestically made weapons stocks and abandon further production (1990s).
Nuclear weapons have been detonated on over two thousand occasions for testing purposes and demonstrations.
After the collapse of the Soviet Union in 1991 and the resultant end of the Cold War, the threat of a major nuclear war between the two nuclear superpowers was generally thought to have declined. Since then, concern over nuclear weapons has shifted to the prevention of localized nuclear conflicts resulting from nuclear proliferation, and the threat of nuclear terrorism.

The possibility of using nuclear weapons in war is usually divided into two subgroups, each with different effects and potentially fought with different types of nuclear armaments.
The first, a limited nuclear war (sometimes attack or exchange), refers to a small-scale use of nuclear weapons by two (or more) belligerents. A "limited nuclear war" could include targeting military facilities - either as an attempt to pre-emptively cripple the enemy's ability to attack as a defensive measure, or as a prelude to an invasion by conventional forces, as an offensive measure. This term could apply to any small-scale use of nuclear weapons that may involve military or civilian targets (or both).[dubious – discuss][according to whom?]
The second, a full-scale nuclear war, could consist of large numbers of nuclear weapons used in an attack aimed at an entire country, including military, economic, and civilian targets. Such an attack would almost certainly destroy the entire economic, social, and military infrastructure of the target nation, and would probably have a devastating effect on Earth's biosphere.
Some Cold War strategists such as Henry Kissinger argue that a limited nuclear war could be possible between two heavily armed superpowers (such as the United States and the Soviet Union). Some predict, however, that a limited war could potentially "escalate" into a full-scale nuclear war. Others[who?] have called limited nuclear war "global nuclear holocaust in slow motion" - arguing that once such a war took place, others would be sure to follow over a period of decades, effectively rendering the planet uninhabitable in the same way that a "full-scale nuclear war" between superpowers would, only taking a much longer (and arguably more agonizing) path to the same result.
Even the most optimistic predictions of the effects of a major nuclear exchange foresee the death of many millions of victims within a very short period of time. More pessimistic predictions argue that a full-scale nuclear war could potentially bring about the extinction of the human race, or at least its near extinction, with only a relatively small number of survivors (mainly in remote areas) and a reduced quality of life and life expectancy for centuries afterward. Such a horrific catastrophe would almost certainly cause permanent damage to most complex life on the planet, its ecosystems, and the global climate - particularly if predictions about the production of a nuclear winter are accurate.
A study presented at the annual meeting of the American Geophysical Union in December 2006 asserted that even a small-scale regional nuclear war could produce as many direct fatalities as all of World War II and disrupt the global climate for a decade or more. In a regional nuclear conflict scenario in which two opposing nations in the subtropics each used 50 Hiroshima-sized nuclear weapons (ca. 15 kiloton each) on major population centers, the researchers predicted fatalities ranging from 2.6 million to 16.7 million per country. Also, they estimated that as much as five million tons of soot could be released, producing a cooling of several degrees over large areas of North America and Eurasia (including most of the grain-growing regions). The cooling would last for years and could be "catastrophic", according to the researchers.
Either a limited or full-scale nuclear exchange could occur during an accidental nuclear war, in which the use of nuclear weapons is triggered unintentionally. Postulated triggers for this scenario have included malfunctioning early warning devices and/or targeting computers, deliberate malfeasance by rogue military commanders, consequences of an accidental straying of warplanes into enemy airspace, reactions to unannounced missile tests during tense diplomatic periods, reactions to military exercises, mistranslated or misscommunicated messages, and others. A number of these scenarios actually occurred during the Cold War, though none resulted in the use of nuclear weapons.Many such scenarios have been depicted in popular culture, such as in the 1962 novel Fail-Safe (released as a film in 1964), and the film Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb, also released in 1964.

During the final stages of World War II in 1945, the United States conducted two atomic bombings against the Japanese cities of Hiroshima and Nagasaki, the first on August 6, 1945, and the second on August 9, 1945. These two events are the only use of nuclear weapons in war to date.

For six months before the atomic bombings, the United States intensely fire-bombed 67 Japanese cities. Together with the United Kingdom and the Republic of China, the United States called for the unconditional surrender of Japan in the Potsdam Declaration issued July 26, 1945. The Japanese government ignored this ultimatum. By executive order of President Harry S. Truman, the U.S. employed the uranium-type nuclear weapon code named "Little Boy" on the city of Hiroshima on Monday, August 6, 1945, followed three days later by the detonation of the plutonium-type weapon code named "Fat Man" over the city of Nagasaki on August 9.

Within the first two to four months after the bombings, acute effects killed 90,000–166,000 people in Hiroshima and 60,000–80,000 in Nagasaki, with roughly half of the deaths in each city occurring in the first 24 hours. The Hiroshima prefectural health department estimates that - of the people who died on the day of the detonation - 60% died from flash or flame burns, 30% from falling or flying debris, and 10% from other causes. During the following months, large numbers died from the chronic effects of burns, radiation sickness, and other injuries, compounded by illnesses. In a U.S. estimate of the total immediate and short-term causes of death, 15–20% died from radiation sickness, 20–30% from flash burns, and 50–60% from other injuries, compounded by illnesses.In both cities, most of the dead were civilians.

Six days after the detonation over Nagasaki, on August 15, 1945, Japan announced its surrender to the Allied Powers, signing the Instrument of Surrender on September 2, 1945, officially ending the Pacific War and, therefore, World War II, as Germany had already signed its Instrument of Surrender on May 7, 1945, ending the war in Europe. The two atomic bombings led, in part, to post-war Japan's adopting of the Three Non-Nuclear Principles, which forbade the nation from developing nuclear armaments.The role of the bombings in the surrender of Japan, the ethical justification of the US for using them, as well as their strategic importance, is still hotly debated.

Though the USSR had nuclear weapon capabilities in the beginning of the Cold War, the US still had an advantage in terms of bombers and weapons. In any exchange of hostilities, the US would have been capable of bombing the USSR, while the USSR would have more difficulty carrying out the reverse mission.
The widespread introduction of jet-powered interceptor aircraft upset this imbalance somewhat by reducing the effectiveness of the US bomber fleet. In 1949 Curtis LeMay was placed in command of the Strategic Air Command and instituted a program to update the bomber fleet to one that was all-jet. During the early 1950s the B-47 and B-52 were introduced, providing the ability to bomb the USSR more easily. Before the development of a capable strategic missile force in the Soviet Union, much of the war-fighting doctrine held by western nations revolved around using a large number of smaller nuclear weapons used in a tactical role. It is debatable whether such use could be considered "limited" however, because it was believed that the US would use their own strategic weapons (mainly bombers at the time) should the USSR deploy any kind of nuclear weapon against civilian targets. Douglas MacArthur, an American general, was fired by President Harry Truman, partially because he persistently requested permission to use his own discretion in deciding whether to use atomic weapons on the People's Republic of China in 1951 during the Korean War.[22][dead link] Mao Zedong, China's communist leader, gave the impression that he would welcome a nuclear war with the capitalists because it would annihilate their imperialist system.[23][24]
Let us imagine how many people would die if war breaks out. There are 2.7 billion people in the world, and a third could be lost. If it is a little higher it could be half ... I say that if the worst came to the worst and one-half dies, there will still be one-half left, but imperialism would be razed to the ground and the whole world would become socialist. After a few years there would be 2.7 billion people again.
— Mao Zedong, 1957

Several scares about the increasing ability of the USSR's strategic bomber forces surfaced during the 1950s. The defensive response by the US was to deploy a fairly strong "layered defense" consisting of interceptor aircraft and anti-aircraft missiles, like the Nike, and guns, like the Skysweeper, near larger cities. However, this was a small response compared to the construction of a huge fleet of nuclear bombers. The principal nuclear strategy was to massively penetrate the USSR. Because such a large area could not be defended against this overwhelming attack in any credible way, the USSR would lose any exchange.
This logic became ingrained in US nuclear doctrine and persisted for much of the duration of the Cold War. As long as the strategic US nuclear forces could overwhelm their USSR counterparts, a Soviet preemptive strike could be averted. Moreover, the USSR could not afford to build any reasonable counterforce, as the economic output of the United States was far larger than that of the Soviets, and they would be unable to achieve "nuclear parity".
Soviet nuclear doctrine, however, did not match US nuclear doctrine.[26] Soviet planning expected a large-scale nuclear exchange, followed by a "conventional war" which itself would involve heavy use of tactical nuclear weapons. Unfortunately, US doctrine rather assumed that Soviet doctrine was similar, with the mutual in Mutually Assured Destruction necessarily requiring that the other side see things in much the same way, rather than believing - as the Soviets did - that they could fight a large-scale, "combined nuclear and conventional" war.
A revolution in nuclear strategic thought occurred with the introduction of the intercontinental ballistic missile (ICBM), which the USSR first successfully tested in August 1957. In order to deliver a warhead to a target, a missile was much faster and more cost-effective than a bomber, and enjoyed a higher survivability due to the enormous difficulty of interception of the ICBMs (due to their high altitude and extreme speed). The USSR could now afford to achieve nuclear parity with the US in terms of raw numbers, although for a time, they appeared to have chosen not to.
Photos of Soviet missile sites set off a wave of panic in the US military, something the launch of Sputnik would do for the American public a few months later. Politicians, notably then-US Senator John F. Kennedy suggested that a "missile gap" existed between the Soviets and the US. The US military gave missile development programs the highest national priority, and several spy aircraft and reconnaissance satellites were designed and deployed to observe Soviet progress.
Early ICBMs and bombers were relatively inaccurate, which led to the concept of countervalue strikes — attacks directly on the enemy population, which would theoretically lead to a collapse of the enemy's will to fight. During the Cold War the USSR invested in extensive protected civilian infrastructure, such as large "nuclear-proof" bunkers and non-perishable food stores. In the US, by comparison, smaller scale civil defense programs were instituted starting in the 1950s, where schools and other public buildings had basements stocked with non-perishable food supplies, canned water, first aid, and dosimeter and Geiger counter radiation-measuring devices. Many of the locations were given "Fallout Shelter" designation signs. Also, CONELRAD Radio information systems were adopted, whereby the commercial radio sector would broadcast on two AM frequencies in the event of a Civil Defense (CD) emergency. These two frequencies can still be seen on 1950s-vintage radios on online auction sites and museums, with many of these radios are still in use on tabletops across America. Also, the occasional backyard fallout shelter was built by private individuals.

The U.S. conducted hundreds of nuclear tests at the Nevada Test Site.