answer:I think “overwhelmed by” reflects the emotional state of the victims. That is, they felt overwhelmed. Alternatively, they might be __disheartened__ by the amount of work. “Overwhelmed with,” on the other hand, seems more to deal with the state of __things__. That is, the volume of work would not fit into the container available for it (time or space.) Alternatively, the work might __exceed the capacity__ they had to get it done.