I think the answer is the reason for his absence is quite simple to understand.
what is the topic of essay? you have not mentioned the topic , then what is the purpose of giving all the other information.
Maybe the answer is in oregon, I'm not exactly sure.
A Theme is a Message the the Author wants to get across to his readers
A Central Idea is a element in a story that ties together the imformation
I Hope the Helps
√ Dante√
The topic sentence is number 1