This question is kind of hard to answer.
Out of the countries listed, these countries are known to have nuclear weapons. ( I suppose with Israel it is a sort "well...we're not going to admit it but...)
- Israel
- Pakistan
- Russia
- United Kingdom
- India
- China
North Korea like to make grandiose claims, but in a real world scenario, wouldn't survive without China.
Again, "strongest" is very open to interperation. Most men? Most technologically advanced?
In a survival war, how do you consider nuclear weapons in your question?