A thesis statement should give you a good place to work from. If it is too general it is difficult to develop.

To correct the existing statement which would then be grammatically correct and suitable for use from "The fall of Jerusalem in A.D. 70 and the devastating effects on its people" you could simply say "The fall of Jerusalem in A.D.70 had a devastating effect on its people." It would perhaps be better to take your idea and adjust it a little so that it  

will control the direction and development of the paper

 such as,

The fall of Jerusalem in A.D.70 had a devastating effect on its people, who lacked the leadership skills to face battle, and their poor discipline prevented them from facing the enemy effectively; thereby crushing their resistance.