nuclear weapons destructive power is exaggerated in minds of most people, they think that biggest nuclear powers are equipped with some giga powerful 50 megaton nuclear weapons but in reality many warheads equipped in ICBMs/SLBMs are equal or less than 500 kilotons.
Many people think in case of nuclear war it's like in movies, countries just strike cities/towns for the sake of it, even if there's nothing worth destroying.
Africa and South America has no nuclear weapons, so they will survive for the most part, even eurasia and north america won't be as doomed as many think.
Only U.S can win nuclear war because they're the only country having high chances of successful first nuclear disarming strike.