Part 3: Countries with proven Nuclear Capabilities

Countries with proven Nuclear Capabilities
Nuclear bombs are complex devices.  Having designed one, it is not guaranteed that it would work as expected.  Testing the device is necessary and sophisticated monitoring procedures are followed to ascertain the results of the test. International community is also able to detect and deduce much useful information about any tests that are performed.
The following couple of pictures show different types of tests and where the tests have been performed and the countries responsible.

Notice that the yield of the tests has been 510 MT which is almost 100 times all the bombs used in WWII
The nuclear arsenal is huge.  At the peak of the arms race - in 1970s - USSR and USA had about 80,000 warheads.  Assuming a warhead of 1 MT explosive capacity that is 80,000 MT of TNT equivalent or 16,000 times the bombs used in WWII.  This is more than sufficient to destroy all population centres in the world.