These days it seems every World power and some smaller nations have access to Nuclear weapons.
After the U.S succesfully detonated the first and only nuclear Bombs to have ever been used in War up to this point in Time,
Every major nation has aquired nukes. In the event of a nuclear Strike againts a nation every major city is a prime target. in the case of the U.S you can say that Some nations have their missles pointed at Washington D.C for it is the capitol of what some would call "the most powerfull nation in the world". in recent and up to 60 years ago the U.S has angered many people so the possibility of a nuclear strike againts the Capitol is ever prevelant.

A Nuclear bomb Explosion has at least 3 phases, An extremly blinding noiseless flash, a devastating shockvave, and massive fires evry where. In John Herseys account of hiroshima survivors Tittled " Hiroshima" the first phase is described as "everything flashed whiter than any white she had ever seen" by one of the survivors.
The second phase, the shockvave caused many buildinds to collapes such Dr fujis clinic "the hospital leaned behind his rising and with a terrible ripping noise toppled into the river".
The Last Phase was the fire that ravaged the whole city. Since the Nuclear bombs fission produces heat up to 7000 degrees fareinheit, anything not directly blown away or incinerated would catch fire.
During the initial moment of the attack all that would be vivible would be the noisless flash. After eveything gets blown away the still standing structures would catch fire. If the explosion itself doesnt kill you then the Radiation produced will. Gamma and nuetron Rays produced by the explosion have tremendous penetrating power for it takes a Foot of lead to stop them.These Rays cause serious damage to humans and wildlife alike as they target individual cells and kill them making them unable to reproduce. And because of their penetration power they can affect internal organs and the nervous system which could kill people. Anyone not killed by the radiation could suffer serious medical problems later on like cancer or becoming sterile.
The city itself would be mostly destroyed.As seen in hiroshima a few weeks after the explosion plant life growth would be greatly stimulated by the bomb.

As prevoiusly stated Many countries have nuclear power such as Russia,Uk, france , china , North korea, israel, ect. North korea has been bitter ever since The U.S invaded them in the 50s in response to their communist ways and them invading South korea. North korea aquired nukes in 2006. and they are a likely candidate for attempting an attack on the U.s since they seem to hate the U.S. Another likely candidate is China as they control 95% percent of the worlds preciose minerals and are communist but it is very unlikely. The U.S has had problems with the middle east in the past decade as such Iran could also prove to be a treath as stated By Ben Fellers "Obama Confront nuclear threaths on the world Stage". Back in 1945 America was Desperate to End the War with a nation whose culture forbade them to surrender at any cost. America then decided that they needed to prove to japan that they could be completly destroyed at any moment by dropping the bomb on