I am looking for IDEAS, not EXAMPLES on: why does conflict have the greatest impact on the most vulnerable?
If you are looking for explanations, not examples, then I would suggest that the answer is right there in the language of the question.
Being vulnerable really means being open to assault or existing in a state of weakness. Those who are vulnerable are definitively more likely to suffer loss or strife.
If the question is geared toward a comparison where we are asking why some people suffer more during a shared conflict than others, the answer will take on greater nuance - as will the question.
So, are we asking: If the same thing happens to two people, what personal characteristics will determine how vulnerable each person is?
Some of the answer to this question may vary depending on the type of conflict you are considering.
If you are looking at a situation in which a particular culture is suffering conflict due to the breakdown of regional government and infrastructure, some of the services that are going to be most affected by that breakdown may include law enforcement, communications and transportation. Vulnerable sections of the population of the affected area frequently are particularly dependent upon the services that would impacted by this type of breakdown.
If the conflict is directly due to military action between combatants, the most vulnerable population will be the unarmed citizens, frequently including those unable to leave the area due to age or physical infirmity.
If you are considering a conflict between management and factory workers, the most vulnerable would be the family members of the most recently hired laborers, those who will be laid off first from the lowest paying jobs in the factory.