What is responsible for the extreme force in a nuclear bomb?

[LogicalAcid]

What I always thought is that the strong force in each atom, when the nucleus is impacted and is separated, some of the nuclear force is let out. Multiply this by billions, and voila.

 

[cragar]

When a uranium nuclei for example splits , the products are lighter and there is a mass difference so this is converted into energy using E=mc^2 and it also has to do with nuclear binding energy

 

[Dale]

Adding to what cragar said, some of that converted energy will go into high energy electromagnetic radiation (gamma rays), and the rest will go into giving high kinetic energy to the products of the nuclear reaction.