Question

the greatest thert to the world is the belif that someone else will save it

Answer 1

its theft and belief
the increasing dependency on others that if we will do something we do may not be helpful and we leave it to next person

Answer 2

plz start u essay with a question like...
what do you mean by belief ?
    OR
the belief in the above topic refers to the feeling of being certain that something is true.
there are many threts to the world but the most dangerous is the belief that someone else will save or protect.
in other words we can say that these can also be called as dependence
AS in a joint family if all the members of that family depend on the main head of that family, if any trouble occurs either financially or personally other members of that family may not be able to solve it ,as they were totally dependent on the head of the family they will surely may loose they abilites and will not even try to get it out.
IN the same way even our world is in such a belief that others are there to take care of things happening around us.at present our world in the same situation if we won't change this thought now - for sure no one can change if it spread like fire on dried grass.if once human mind become dependent saying that others will do.... not even a single person on this earth can protect themself becoz they seek that others will help them... and they dont realize that others are also thinking in the same way.
so plz change u r mind set 
let the change start from us.