Death is a big inherent danger, so is total destruction of real estate. Radioactive wasteland is another danger. In a full-scale global war, the amount of dust lifted into the atmosphere could block out the sun, resulting in a temperature drop called a nuclear winter.

Radiation

Lots of dust kicked up into the air

Sun is blocked from dust

Nuclear Winter because of cold because of blocked sun

Chance of more bombs being dropped

Life dies because of the cold

All of this is very, very, BAD

Judging by the power of modern day technology I would say that with one drop of a nuke anywhere in the world hundreds of nukes would be dropped in response.

Life would be over, next question?

radiation

explosion

fireballs

mushroom clouds

zombies

mutants