Moreover, the proportion of women among those who join the
extremist group has been increasing dramatically.
a)What is behind it and what exactly is the ISIS estrategy to entice them?
What are the reasons behind such attraction/rise? and what exactly is ISIS strategy
to entice them?
The way it was, one could ask, he meant "what is behind the rise of woman among the group? or what is behind the attraction towards the ISIS group? That is, these are two different questions. So, in (b) I tried to fix the (what seems to me an) ambiguity.
===================On a hand , it treats those who it considers herege in nearly subhuman conditions, as commodities to be exchanged and given as a premium for jihadist warriors.
You should use "on the one hand" followed (at other point of the sentence, or even the paragraph) by on the other hand, to contrast ideas.http://dictionary.cambridge.org/pt/dici ... other-hand
However, I don´t know what you meant, perhaps you wanted to state was "on the other hand" to contrast with some previous information, and not to contrast ideas of this part of the text.
As you see, I didn´t change much on the text, you were almost there, you could express yourself. It just had to retouch some grammar points!