What is the subject of the sentence? To this had to be added...

"This" is the subject of the sentence.

"Among the strengths of" can be read as "among the advantages of."

If the sentence is "this had to be added a loack of incentives and downright hunger", it is perfect normal and well understood. Adding "to" in front of it is rather weird, isn't it? It seems that the "to" is useless here. What does it mean if you don't agree?

lack / had to be added
of > incentives and hunger
to>this ( both prep. phrases)

To this had to be added a loack of incentives and downright hunger. ==>

A lack of incentives and downright hunger had to be added to this. (The 'to' is a preposition.)

(In my opinion, the original text is badly written...)