In this age of technology where no one nation trusts the other, it comes as no surprise that most of them have armed themselves with frightening numbers of nuclear weapons and would readily use them given if the need arises.
There are various types of devices that can be and have been developed as nuclear weapons in the recent times and the top players of the field are undoubtedly The United States of America and Russia. Atomic and hydrogen bombs along with the Gravity bombs are the well known forms of nuclear weapons that have been developed and re-developed over a period of time.
And even though the number of weapons now, as compared to the past decades have almost come down to a third of what were but there is still a huge risk of them being used by their host nations.